Controlling transitions in optically switchable devices

ABSTRACT

Aspects of this disclosure concern controllers and control methods for applying a drive voltage to bus bars of optically switchable devices such as electrochromic devices. Such devices are often provided on windows such as architectural glass. In certain embodiments, the applied drive voltage is controlled in a manner that efficiently drives an optical transition over the entire surface of the electrochromic device. The drive voltage is controlled to account for differences in effective voltage experienced in regions between the bus bars and regions proximate the bus bars. Regions near the bus bars experience the highest effective voltage. In some cases, feedback may be used to monitor an optical transition. In these or other cases, a group of optically switchable devices may transition together over a particular duration to achieve approximately uniform tint states over time during the transition.

CROSS REFERENCE TO RELATED APPLICATION

This application claims benefit of priority to U.S. ProvisionalApplication No. 62/239,776, filed Oct. 9, 2015, and titled “CONTROLLINGTRANSITIONS IN OPTICALLY SWITCHABLE DEVICES,” which is hereinincorporated by reference in its entirety and for all purposes. Thisapplication is also a continuation-in-part of U.S. patent applicationSer. No. 14/900,037, filed Dec. 18, 2015, and titled “CONTROLLINGTRANSITIONS IN OPTICALLY SWITCHABLE DEVICES,” which is a §371 NationalPhase Application of PCT Application No. PCT/US14/43514, filed Jun. 20,2014, and titled “CONTROLLING TRANSITIONS IN OPTICALLY SWITCHABLEDEVICES,” which is a continuation-in-part of U.S. patent applicationSer. No. 13/931,459, filed Jun. 28, 2013, each of which is incorporatedby reference in its entirety and for all purposes.

BACKGROUND

Electrochromic (EC) devices are typically multilayer stacks including(a) at least one layer of electrochromic material, that changes itsoptical properties in response to the application of an electricalpotential, (b) an ion conductor (IC) layer that allows ions, such aslithium ions, to move through it, into and out from the electrochromicmaterial to cause the optical property change, while preventingelectrical shorting, and (c) transparent conductor layers, such astransparent conducting oxides or TCOs, over which an electricalpotential is applied to the electrochromic layer. In some cases, theelectric potential is applied from opposing edges of an electrochromicdevice and across the viewable area of the device. The transparentconductor layers are designed to have relatively high electronicconductances. Electrochromic devices may have more than theabove-described layers such as ion storage or counter electrode layersthat optionally change optical states.

Due to the physics of the device operation, proper function of theelectrochromic device depends upon many factors such as ion movementthrough the material layers, the electrical potential required to movethe ions, the sheet resistance of the transparent conductor layers, andother factors. The size of the electrochromic device plays an importantrole in the transition of the device from a starting optical state to anending optical state (e.g., from tinted to clear or clear to tinted).The conditions applied to drive such transitions can have quitedifferent requirements for different sized devices.

What are needed are improved methods for driving optical transitions inelectrochromic devices.

SUMMARY

Aspects of this disclosure concern controllers and control methods forapplying a drive voltage to bus bars of optically switchable devicessuch as electrochromic devices. Such devices are often provided onwindows such as architectural glass. In certain embodiments, the applieddrive voltage is controlled in a manner that efficiently drives anoptical transition over the entire surface of the optically switchabledevice. The drive voltage is controlled to account for differences ineffective voltage experienced in regions between the bus bars andregions proximate the bus bars. Regions near the bus bars experience thehighest effective voltage.

In some embodiments, a first optical transition may be interrupted by acommand to undergo a second optical transition, for example having adifferent ending optical state than the first optical transition. Incertain embodiments, a group of optically switchable devices may undergoa simultaneous optical transition. Some optically switchable devices inthe group may transition faster than other optically switchable devices.In some such embodiments, the transition on the faster opticallyswitchable device may be broken into smaller transitions that areseparated in time. This may allow the slowest and faster opticallyswitchable devices in the group to transition over approximately thesame switching time, with the various optically switchable devicesdisplaying approximately matching optical states over the course of theoverall transition.

In one aspect of the disclosed embodiments, a method of controlling afirst optical transition and a second optical transition of an opticallyswitchable device is provided, the method including: (a) receiving acommand to undergo the first optical transition from a starting opticalstate to a first ending optical state; (b) applying a first driveparameter to bus bars of the optically switchable device and driving thefirst optical transition for a first duration; (c) before the opticallyswitchable device reaches the first ending optical state: (i) receivinga second command to undergo the second optical transition to a secondending optical state, and (ii) applying a second drive parameter to thebus bars of the optically switchable device and driving the secondoptical transition for a second duration, where the second driveparameter is different from the first drive parameter, where the seconddrive parameter is determined based, at least in part, on the secondending optical state and an amount of charge delivered to the opticallyswitchable device during the first optical transition toward the firstending optical state, and where the second optical transition iscontrolled without considering an open circuit voltage of the opticallyswitchable device.

In some embodiments, the method may further include monitoring an amountof charge delivered to the optically switchable device during the secondoptical transition to the second ending optical state, and ceasing toapply the second drive parameter to bus bars of the optically switchabledevice based, at least in part, on the amount of charge delivered to theoptically switchable device during the second optical transition to thesecond ending optical state. In some cases, (c)(ii) may include: after(i), determining the amount of charge delivered to the opticallyswitchable device during the first optical transition toward the firstending optical state, determining a target charge count that isappropriate for causing the optically switchable device to switch fromthe starting optical state to the second ending optical state,monitoring an amount of charge delivered to the optically switchabledevice during the second optical transition to the second ending opticalstate, and applying the second drive parameter to the bus bars of theoptically switchable device until a net amount of charge delivered tothe device during the first and second optical transitions reaches thetarget charge count. In these or other embodiments, (c)(ii) may include:determining or estimating an instantaneous optical state of theoptically switchable device when the second command was received in(c)(i) based, at least in part, on the amount of charge delivered to theoptically switchable device during the first optical transition towardthe first ending optical state, determining a target charge count thatis appropriate for causing the optically switchable device to switchfrom its instantaneous optical state to the second ending optical state,monitoring an amount of charge delivered to the optically switchabledevice during the second optical transition to the second ending opticalstate, and applying the second drive parameter to the bus bars of theoptically switchable device until the charge delivered to the opticallyswitchable device during the second optical transition reaches thetarget charge count.

Driving the first optical transition in (b) may include: applying thefirst drive parameter to the bus bars of the optically switchabledevice, determining a target open circuit voltage appropriate forswitching the optically switchable device from the starting opticalstate to the first ending optical state, and determining a target chargecount appropriate for switching the optically switchable device from thestarting optical state to the first ending optical state, periodicallydetermining an open circuit voltage between the bus bars of theoptically switchable device, and periodically determining the amount ofcharge delivered to the optically switchable device during the firsttransition toward the first ending optical state, and periodicallycomparing the determined open circuit voltage to a target open circuitvoltage and periodically comparing the amount of charge delivered to theoptically switchable device during the first transition toward the firstending optical state to a first target charge count. In variousembodiments, the method may further include: (d) before the opticallyswitchable device reaches the second ending optical state: (i) receivinga third command to undergo a third optical transition to a third endingoptical state, and (ii) applying a third drive parameter to the bus barsof the optically switchable device and driving the third opticaltransition for a third duration, where the third drive parameter isdifferent from the second drive parameter, where the third driveparameter is determined based, at least in part, on the third endingoptical state and an amount of charge delivered to the opticallyswitchable device during the first optical transition toward the firstending optical state and during the second optical transition toward thesecond ending optical state, and where the third optical transition iscontrolled without considering an open circuit voltage of the opticallyswitchable device.

In another aspect of the disclosed embodiments, an apparatus forcontrolling a first optical transition and a second optical transitionof an optically switchable device is provided, the apparatus including:a processor designed or configured to: (a) receive a command to undergothe first optical transition from a starting optical state to a firstending optical state; (b) apply a first drive parameter to bus bars ofthe optically switchable device and drive the first optical transitionfor a first duration; (c) before the optically switchable device reachesthe first ending optical state: (i) receive a second command to undergothe second optical transition to a second ending optical state, (ii)apply a second drive parameter to the bus bars of the opticallyswitchable device and drive the second optical transition for a secondduration, where the second drive parameter is different from the firstdrive parameter, where the second drive parameter is determined based,at least in part, on the second ending optical state and an amount ofcharge delivered to the optically switchable device during the firstoptical transition toward the first ending optical state, and where theprocessor is designed or configured to control the second opticaltransition without considering an open circuit voltage of the opticallyswitchable device.

In some such embodiments, the processor may be designed or configured tomonitor an amount of charge delivered to the optically switchable deviceduring the second optical transition to the second ending optical state,and cease to apply the second drive parameter to bus bars of theoptically switchable device based, at least in part, on the amount ofcharge delivered to the optically switchable device during the secondoptical transition to the second ending optical state. In some cases,the processor may be designed or configured, in (c)(ii) to: after (i),determine the amount of charge delivered to the optically switchabledevice during the first optical transition toward the first endingoptical state, determine a target charge count that is appropriate forcausing the optically switchable device to switch from the startingoptical state to the second ending optical state, monitor an amount ofcharge delivered to the optically switchable device during the secondoptical transition to the second ending optical state, and apply thesecond drive parameter to the bus bars of the optically switchabledevice until a net amount of charge delivered to the device during thefirst and second optical transitions reaches the target charge count.

In certain implementations, the processor may be designed or configured,in (c)(ii), to determine or estimate an instantaneous optical state ofthe optically switchable device when the second command was received in(c)(i) based, at least in part, on the amount of charge delivered to theoptically switchable device during the first optical transition towardthe first ending optical state, determine a target charge count that isappropriate for causing the optically switchable device to switch fromits instantaneous optical state to the second ending optical state,monitor an amount of charge delivered to the optically switchable deviceduring the second optical transition to the second ending optical state,and apply the second drive parameter to the bus bars of the opticallyswitchable device until the charge delivered to the optically switchabledevice during the second optical transition reaches the target chargecount.

To drive the first optical transition in (b), the processor may bedesigned or configured to: apply the first drive parameter to the busbars of the optically switchable device, determine a target open circuitvoltage appropriate for switching the optically switchable device fromthe starting optical state to the first ending optical state, anddetermine a target charge count appropriate for switching the opticallyswitchable device from the starting optical state to the first endingoptical state, periodically determine an open circuit voltage betweenthe bus bars of the optically switchable device, and periodically orcontinuously determine the amount of charge delivered to the opticallyswitchable device during the first transition toward the first endingoptical state, and periodically compare the determined open circuitvoltage to a target open circuit voltage and periodically compare theamount of charge delivered to the optically switchable device during thefirst transition toward the first ending optical state to a first targetcharge count. In some embodiments, the processor may be designed orconfigured to receive additional commands to undergo additional opticaltransitions before the optically switchable device reaches the secondending optical state, and apply additional drive parameters to bus barsof the optically switchable device, where the additional driveparameters are determined based, at least in part, on target endingoptical states for the additional optical transitions and an amount ofcharge delivered to the optically switchable device between the timethat the optically switchable device transitions from its startingoptical state and the time that the additional optical transitionsbegin, where the processor is designed or configured to control theadditional optical transitions without considering the open circuitvoltage of the optically switchable device.

In another aspect of the disclosed embodiments, an apparatus forcontrolling optical transitions in an optically switchable device isprovided, the apparatus including: a processor designed or configuredto: (a) measure an open circuit voltage of the optically switchabledevice, and determine a tint state of the optically switchable devicebased on the open circuit voltage; (b) control a first opticaltransition from a first starting optical state to a first ending opticalstate in response to a first command by: (i) applying a first driveparameter to bus bars of the optically switchable device for a firstduration to transition from the first starting optical state to thefirst ending optical state, (ii) before the first optical transition iscomplete, periodically determining an open circuit voltage between thebus bars of the optically switchable device, and periodicallydetermining an amount of charge delivered to the optically switchabledevice during the first optical transition, (iii) comparing the opencircuit voltage to a target open circuit voltage for the first opticaltransition, and comparing the amount of charge delivered to theoptically switchable device during the first optical transition to atarget charge count for the first optical transition, and (iv) ceasingto apply the first drive parameter to the bus bars of the opticallyswitchable device when (1) the open circuit voltage reaches the targetopen circuit voltage for the first optical transition, and (2) theamount of charge delivered to the optically switchable device during thefirst optical transition reaches the target charge count for the firstoptical transition, the first optical transition occurring withoutreceiving an interrupt command; and (c) control a second opticaltransition and a third optical transition, the third optical transitionbeginning before the second optical transition is complete, by: (i)receiving a second command to undergo the second optical transition froma second starting optical state to a second ending optical state; (ii)applying a second drive parameter to bus bars of the opticallyswitchable device and driving the second optical transition for a secondduration; (iii) before the optically switchable device reaches thesecond ending optical state: (1) receiving a third command to undergothe third optical transition to a third ending optical state, (2)applying a third drive parameter to the bus bars of the opticallyswitchable device and driving the third optical transition for a thirdduration, where the third drive parameter is different from the seconddrive parameter, where the third drive parameter is determined based, atleast in part, on the third ending optical state and an amount of chargedelivered to the optically switchable device during the second opticaltransition toward the second ending optical state, and where the thirdoptical transition is controlled without considering an open circuitvoltage of the optically switchable device.

In another aspect of the disclosed embodiments, a method for controllingan optical transition in an optically switchable device from a startingoptical state to an ending optical state is provided, the methodincluding: (a) applying a drive voltage to bus bars of the opticallyswitchable device for a duration to cause the optically switchabledevice to transition toward the ending optical state; (b) measuring anopen circuit voltage between the bus bars of the optically switchabledevice; (c) comparing the open circuit voltage to a target open circuitvoltage for the optical transition; (d) comparing the open circuitvoltage to a safe voltage limit for the optically switchable device, andeither (i) increasing the drive voltage in cases where the open circuitvoltage is less than the safe voltage limit for the optically switchabledevice, or (ii) decreasing the drive voltage in cases where the opencircuit voltage is greater than the safe voltage limit for the opticallyswitchable device; (e) repeating at least operations (a)-(c) at leastonce; and (f) determining that the open circuit voltage has reached thetarget open circuit voltage, ceasing application of the drive voltage tothe bus bars of the optically switchable device, and applying a holdvoltage to the bus bars of the optically switchable device to therebymaintain the ending optical state.

In some embodiments, (b) may further include measuring an amount ofcharge delivered to the device over the course of the opticaltransition, (c) may include comparing the amount of charge delivered tothe device over the course of the optical transition to a target chargecount for the optical transition, and (f) may include determining thatthe amount of charge delivered to the optically switchable device hasreached the target charge count before applying the hold voltage to thebus bars of the optically switchable device.

In another aspect of the disclosed embodiments, a method oftransitioning a group of optically switchable devices is provided, themethod including: (a) receiving a command to transition the group ofoptically switchable devices to an ending optical state, where the groupincludes a slowest optically switchable device and a faster opticallyswitchable device, where the slowest optically switchable device and thefaster optically switchable device are different sizes and/or havedifferent switching properties; (b) determining a switching time for thegroup of optically switchable devices, the switching time being a timerequired for the slowest optically switchable device to reach the endingoptical state; (c) transitioning the slowest optically switchable deviceto the ending optical state; and (d) during (c), transitioning thefaster optically switchable device to the ending optical state with oneor more pauses during transition, the one or more pauses chosen in timeand duration so as to approximately match an optical state of the fasteroptically switchable device with an optical state of the slowestoptically switchable device during (c).

In some embodiments, the one or more pauses may include at least twopauses. The time and duration of the one or more pauses may bedetermined automatically using an algorithm. In some cases, thedurations of the one or more pauses may be determined based on a lookuptable. The lookup table may include information regarding a size of eachoptically switchable device in the group and/or a switching time foreach optically switchable device in the group.

In various implementations, a transition on the slowest opticallyswitchable device may be monitored using feedback obtained during thetransition on the slowest optically switchable device. The feedbackobtained during the transition on the slowest optically switchabledevice may include one or more parameters selected from the groupconsisting of: an open circuit voltage, a current measured in responseto an applied voltage, and a charge or charge density delivered to theslowest optically switchable device. In one example, the feedbackobtained during the transition on the slowest optically switchabledevice includes the open circuit voltage and the charge or chargedensity delivered to the slowest optically switchable device. In theseor other embodiments, the transition on the faster optically switchabledevice may be monitored using feedback obtained during the transition onthe faster optically switchable device. The feedback obtained during thetransition on the faster optically switchable device may include one ormore parameters selected from the group consisting of: an open circuitvoltage, a current measured in response to an applied voltage, and acharge or charge density delivered to the faster optically switchabledevice. In one example, the feedback obtained during the transition onthe faster optically switchable device includes the charge or chargedensity delivered to the faster optically switchable device, and doesnot include the open circuit voltage, nor the current measured inresponse to the applied voltage.

The group of optically switchable devices may include any number ofoptically switchable devices, which may each be of any size. In someembodiments, the group of optically switchable devices may include twoor more faster optically switchable devices, and transitioning in (d)may be staggered for the two or more faster optically switchable devicessuch that at least one of the faster optically switchable devices pauseswhile at least one other of the faster optically switchable devicestransitions. In these or other embodiments, the group of opticallyswitchable devices may include optically switchable devices of at leastthree different sizes.

The method may further include (e) applying a hold voltage to eachdevice of the group of optically switchable devices as each devicereaches the ending optical state. In some cases, the method may include:in response to receiving a command to transition the group of opticallyswitchable devices to a second ending optical state before the group ofoptically switchable devices reaches the ending optical state,transitioning the slowest optically switchable device and the fasteroptically switchable device to the second ending optical state withoutany pauses.

In some embodiments, during pausing in (d), open circuit conditions maybe applied to the faster optically switchable device. In otherembodiments, the method may further include measuring an open circuitvoltage on the faster optically switchable device, and during pausing in(d), the measured open circuit voltage may be applied to the fasteroptically switchable device. In another embodiment, during pausing in(d), a pre-determined voltage may be applied to the faster opticallyswitchable device.

The slowest optically switchable device may transition to the endingoptical state without pausing in some implementations.

In another aspect of the disclosed embodiments, a method oftransitioning a group of optically switchable devices is provided, themethod including: (a) receiving a command to transition the group ofoptically switchable devices to an ending optical state, where the groupincludes a slowest optically switchable device and a faster opticallyswitchable device, where the slowest optically switchable device and thefaster optically switchable device are different sizes and/or havedifferent switching properties; (b) determining a switching time for thegroup of optically switchable devices, the switching time being a timerequired for the slowest optically switchable device to reach the endingoptical state; (c) transitioning the slowest optically switchable deviceto the ending optical state; (d) during (c), transitioning the fasteroptically switchable device to an intermediate optical state; (e) during(c) and after (d), maintaining the intermediate optical state on thefaster optically switchable device for a duration; (f) during (c) andafter (e), transitioning the faster optically switchable device to theending optical state, where the duration in (e) is chosen so as toapproximately match an optical state of the faster optically switchabledevice with an optical state of the slowest optically switchable deviceduring (c).

In certain embodiments, the method may include during (c) and before(f), transitioning the faster optically switchable device to a secondintermediate optical state, and then maintaining the second intermediateoptical state for a second duration. In some cases, the duration during(e) may be determined automatically using an algorithm. In some othercases, the duration during (e) may be determined automatically based ona lookup table.

The various transitions may be monitored using feedback. For example, insome embodiments, a transition on the slowest optically switchabledevice may be monitored using feedback obtained during the transition onthe slowest optically switchable device. The feedback obtained duringthe transition on the slowest optically switchable device may includeone or more parameters selected from the group consisting of: an opencircuit voltage, a current measured in response to an applied voltage,and a charge or charge density delivered to the slowest opticallyswitchable device during the transition on the slowest opticallyswitchable device. In a particular example, the feedback obtained duringthe transition on the slowest optically switchable device includes theopen circuit voltage and the charge or charge density delivered to theslowest optically switchable device. In these or other embodiments,during (f) a transition on the faster optically switchable device to theending optical state may be monitored using feedback obtained on thefaster optically switchable device during (f). For example, the feedbackobtained on the faster optically switchable device during (f) mayinclude one or more parameters selected from the group consisting of: anopen circuit voltage, a current measured in response to an appliedvoltage, and a charge or charge density delivered to the fasteroptically switchable device. In a particular example, the feedbackobtained on the faster optically switchable device during (f) mayinclude the open circuit voltage and the charge or charge densitydelivered to the slowest optically switchable device.

The group of optically switchable devices may include any number ofoptically switchable devices, which may each be of any size. In someembodiments, the group of optically switchable devices may include twoor more faster optically switchable devices, and transitioning in (d)and (f) and maintaining in (e) may be staggered for the two or morefaster optically switchable devices such that at least one of the fasteroptically switchable devices maintains its intermediate optical state in(e) while at least one other of the faster optically switchable devicestransitions in (d) and/or (e). In some embodiments, the group ofoptically switchable devices may include optically switchable devices ofat least three different sizes.

In some embodiments, during maintaining the intermediate optical statein (e), open circuit conditions may be applied to the faster opticallyswitchable device. In some other embodiments, the method may includemeasuring an open circuit voltage on the faster optically switchabledevice, and during maintaining the intermediate optical state in (e),the measured open circuit voltage may be applied to the faster opticallyswitchable device. In some other embodiments, during maintaining theintermediate optical state in (e), a pre-determined voltage may beapplied to the faster optically switchable device.

The slowest optically switchable device may transition to the endingoptical state without stopping at any intermediate optical states. Insome cases, the method may include (g) applying a hold voltage to eachdevice of the group of optically switchable devices as each devicereaches the ending optical state.

In another aspect of the disclosed embodiments, a control system forcontrolling transitions on a group of optically switchable devices isprovided, the control system comprising: one or more processorscomprising instructions for: (a) receiving a command to transition thegroup of optically switchable devices to an ending optical state,wherein the group comprises a slowest optically switchable device and afaster optically switchable device, wherein the slowest opticallyswitchable device and the faster optically switchable device aredifferent sizes and/or have different switching properties; (b)determining a switching time for the group of optically switchabledevices, the switching time being a time required for the slowestoptically switchable device to reach the ending optical state; (c)transitioning the slowest optically switchable device to the endingoptical state; and (d) during (c), transitioning the faster opticallyswitchable device to the ending optical state with one or more pausesduring transition, the one or more pauses chosen in time and duration soas to approximately match an optical state of the faster opticallyswitchable device with an optical state of the slowest opticallyswitchable device during (c).

In some embodiments, the one or more pauses may include at least twopauses. The time and duration of the one or more pauses may bedetermined automatically using an algorithm. In some other cases, thedurations of the one or more pauses may be determined based on a lookuptable. The lookup table may include information regarding a size of eachoptically switchable device in the group and/or a switching time foreach optically switchable device in the group.

In certain implementations, the one or more processors may includeinstructions for monitoring a transition on the slowest opticallyswitchable device using feedback obtained during the transition on theslowest optically switchable device. The feedback obtained during thetransition on the slowest optically switchable device may include one ormore parameters selected from the group consisting of: an open circuitvoltage, a current measured in response to an applied voltage, and acharge or charge density delivered to the slowest optically switchabledevice. In one example, the feedback obtained during the transition onthe slowest optically switchable device may include the open circuitvoltage and the charge or charge density delivered to the slowestoptically switchable device. In these or other embodiments, the one ormore processors may include instructions for monitoring the transitionon the faster optically switchable device using feedback obtained duringthe transition on the faster optically switchable device. For instance,the feedback obtained during the transition on the faster opticallyswitchable device may include one or more parameters selected from thegroup consisting of: an open circuit voltage, a current measured inresponse to an applied voltage, and a charge or charge density deliveredto the faster optically switchable device. In one example, the feedbackobtained during the transition on the faster optically switchable devicemay include the charge or charge density delivered to the fasteroptically switchable device, and does not include the open circuitvoltage, nor the current measured in response to the applied voltage.

The group of optically switchable devices may include any number ofoptically switchable devices. In some embodiments, the group ofoptically switchable devices may include two or more faster opticallyswitchable devices, and transitioning in (d) may be staggered for thetwo or more faster optically switchable devices such that at least oneof the faster optically switchable devices pauses while at least oneother of the faster optically switchable devices transitions. In someembodiments, the group of optically switchable devices may includeoptically switchable devices of at least three different sizes. Invarious cases, the instructions may further include: (e) applying a holdvoltage to each device of the group of optically switchable devices aseach device reaches the ending optical state. In these or other cases,the instructions may further include: in response to receiving a commandto transition the group of optically switchable devices to a secondending optical state before the group of optically switchable devicesreaches the ending optical state, transitioning the slowest opticallyswitchable device and the faster optically switchable device to thesecond ending optical state without any pauses.

In some implementations, during pausing in (d), open circuit conditionsare applied to the faster optically switchable device. In some otherimplementations, the instructions may further include measuring an opencircuit voltage on the faster optically switchable device, and duringpausing in (d), the measured open circuit voltage may be applied to thefaster optically switchable device. In some other implementations,during pausing in (d), a pre-determined voltage may be applied to thefaster optically switchable device. In various embodiments, the slowestoptically switchable device may transition to the ending optical statewithout pausing.

In another aspect of the disclosed embodiments, a control system forcontrolling transitions on a group of optically switchable devices isprovided, the control system including: one or more processors includinginstructions for: (a) receiving a command to transition the group ofoptically switchable devices to an ending optical state, where the groupincludes a slowest optically switchable device and a faster opticallyswitchable device, where the slowest optically switchable device and thefaster optically switchable device are different sizes and/or havedifferent switching properties; (b) determining a switching time for thegroup of optically switchable devices, the switching time being a timerequired for the slowest optically switchable device to reach the endingoptical state; (c) transitioning the slowest optically switchable deviceto the ending optical state; (d) during (c), transitioning the fasteroptically switchable device to an intermediate optical state; (e) during(c) and after (d), maintaining the intermediate optical state on thefaster optically switchable device for a duration; and (f) during (c)and after (e), transitioning the faster optically switchable device tothe ending optical state, where the duration in (e) is chosen so as toapproximately match an optical state of the faster optically switchabledevice with an optical state of the slowest optically switchable deviceduring (c).

In some embodiments, the instructions may further include: during (c)and before (f), transitioning the faster optically switchable device toa second intermediate optical state, and then maintaining the secondintermediate optical state for a second duration. The duration during(e) may be determined automatically using an algorithm. In some othercases, the duration during (e) may be determined automatically based ona lookup table.

In various implementations, the one or more processors may be configuredto monitor a transition on the slowest optically switchable device usingfeedback obtained during the transition on the slowest opticallyswitchable device. For example, the feedback obtained during thetransition on the slowest optically switchable device may include one ormore parameters selected from the group consisting of: an open circuitvoltage, a current measured in response to an applied voltage, and acharge or charge density delivered to the slowest optically switchabledevice during the transition on the slowest optically switchable device.In one example, the feedback obtained during the transition on theslowest optically switchable device may include the open circuit voltageand the charge or charge density delivered to the slowest opticallyswitchable device. In these or other embodiments, the one or moreprocessors may be configured to monitor a transition on the fasteroptically switchable device to the ending optical state during (f) usingfeedback obtained on the faster optically switchable device during (f).For example, the feedback obtained on the faster optically switchabledevice during (f) may include one or more parameters selected from thegroup consisting of: an open circuit voltage, a current measured inresponse to an applied voltage, and a charge or charge density deliveredto the faster optically switchable device. In a particular example, thefeedback obtained on the faster optically switchable device during (f)may include the open circuit voltage and the charge or charge densitydelivered to the slowest optically switchable device.

The group of optically switchable devices may include any number ofoptically switchable devices. In certain embodiments, the group ofoptically switchable devices may include two or more faster opticallyswitchable devices, and transitioning in (d) and (f) and maintaining in(e) may be staggered for the two or more faster optically switchabledevices such that at least one of the faster optically switchabledevices maintains its intermediate optical state in (e) while at leastone other of the faster optically switchable devices transitions in (d)and/or (e). In various embodiments, the group of optically switchabledevices may include optically switchable devices of at least threedifferent sizes.

In some embodiments, during maintaining the intermediate optical statein (e), open circuit conditions may be applied to the faster opticallyswitchable device. In some other embodiments, the instructions mayfurther include measuring an open circuit voltage on the fasteroptically switchable device, and during maintaining the intermediateoptical state in (e), the measured open circuit voltage may be appliedto the faster optically switchable device. In some other embodiments,during maintaining the intermediate optical state in (e), apre-determined voltage may be applied to the faster optically switchabledevice.

In various cases, the slowest optically switchable device may transitionto the ending optical state without stopping at any intermediate opticalstates. In a number of embodiments, the instructions may furtherinclude: (g) applying a hold voltage to each device of the group ofoptically switchable devices as each device reaches the ending opticalstate. These and other features will be described in further detailbelow with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically depicts a planar bus bar arrangement.

FIG. 1B presents a simplified plot of the local voltage value on eachtransparent conductive layer as a function of position on the layer

FIG. 1C presents a simplified plot of V_(eff) as a function of positionacross the device

FIG. 2 is a graph depicting voltage and current profiles associated withdriving an electrochromic device from clear to tinted and from tinted toclear.

FIG. 3 is a graph depicting certain voltage and current profilesassociated with driving an electrochromic device from clear to tinted.

FIG. 4A is a graph depicting an optical transition in which a drop inapplied voltage from V_(drive) to V_(hold) results in a net current flowestablishing that the optical transition has proceeded far enough topermit the applied voltage to remain at V_(hold) for the duration of theending optical state.

FIG. 4B is a graph depicting an optical transition in which an initialdrop in applied voltage from V_(drive) to V_(hold) results in a netcurrent flow indicating that the optical transition has not yetproceeded far enough to permit the applied voltage to remain at V_(hold)for the duration of the ending optical state. Therefore the appliedvoltage is returned to V_(drive) for a further period of time beforeagain dropping again to V_(hold) at which point the resulting currentestablishes that the optical transition has proceeded far enough topermit the applied voltage to remain at V_(hold) for the duration of theending optical state.

FIG. 5A is a flow chart depicting a process for probing the progress ofan optical transition and determining when the transition is complete.

FIG. 5B is a flow chart depicting a process for probing the progress ofan optical transition and speeding the transition if it is notprogressing sufficiently fast.

FIGS. 5C-5F are flow charts depicting alternative processes for probingthe progress of an optical transitioning and determining when thetransition is complete.

FIGS. 5G and 5H are flow charts showing methods for controlling anoptical transition using various kinds of feedback modes.

FIG. 5I depicts various graphs describing a number of parameters relatedto optical transitions over time.

FIG. 5J is a flow chart depicting another method for controlling anoptical transition and determining when the transition is complete.

FIGS. 5K-5M present flowcharts for methods of controlling opticaltransitions on groups of optically switchable devices that havedifferent switching rates.

FIGS. 6A and 6B show graphs depicting the total charge delivered overtime and the voltage applied over time during an electrochromictransition when using the method of FIG. 5E to probe and monitor theprogress of the transition, at room temperature (FIG. 6A) and at areduced temperature (FIG. 6B).

FIG. 6C illustrates an electrochromic window having a pair of voltagesensors on the transparent conductive oxide layers according to anembodiment.

FIGS. 7A and 7B present cross-sectional views of an exampleelectrochromic device in operation.

FIGS. 8 and 9 are representations of window controllers and associatedcomponents.

FIG. 10 illustrates a group of optically switchable devices includingone large device and several smaller devices.

FIGS. 11A-C present experimental data related to the method described inFIG. 5K.

DETAILED DESCRIPTION Definitions

An “optically switchable device” is a thin device that changes opticalstate in response to electrical input. It reversibly cycles between twoor more optical states. Switching between these states is controlled byapplying predefined current and/or voltage to the device. The devicetypically includes two thin conductive sheets that straddle at least oneoptically active layer. The electrical input driving the change inoptical state is applied to the thin conductive sheets. In certainimplementations, the input is provided by bus bars in electricalcommunication with the conductive sheets.

While the disclosure emphasizes electrochromic devices as examples ofoptically switchable devices, the disclosure is not so limited. Examplesof other types of optically switchable device include certainelectrophoretic devices, liquid crystal devices, and the like. Opticallyswitchable devices may be provided on various optically switchableproducts, such as optically switchable windows. However, the embodimentsdisclosed herein are not limited to switchable windows. Examples ofother types of optically switchable products include mirrors, displays,and the like. In the context of this disclosure, these products aretypically provided in a non-pixelated format.

An “optical transition” is a change in any one or more opticalproperties of an optically switchable device. The optical property thatchanges may be, for example, tint, reflectivity, refractive index,color, etc. In certain embodiments, the optical transition will have adefined starting optical state and a defined ending optical state. Forexample the starting optical state may be 80% transmissivity and theending optical state may be 50% transmissivity. The optical transitionis typically driven by applying an appropriate electric potential acrossthe two thin conductive sheets of the optically switchable device.

A “starting optical state” is the optical state of an opticallyswitchable device immediately prior to the beginning of an opticaltransition. The starting optical state is typically defined as themagnitude of an optical state which may be tint, reflectivity,refractive index, color, etc. The starting optical state may be amaximum or minimum optical state for the optically switchable device;e.g., 90% or 4% transmissivity. Alternatively, the starting opticalstate may be an intermediate optical state having a value somewherebetween the maximum and minimum optical states for the opticallyswitchable device; e.g., 50% transmissivity.

An “ending optical state” is the optical state of an opticallyswitchable device immediately after the complete optical transition froma starting optical state. The complete transition occurs when opticalstate changes in a manner understood to be complete for a particularapplication. For example, a complete tinting might be deemed atransition from 75% optical transmissivity to 10% transmissivity. Theending optical state may be a maximum or minimum optical state for theoptically switchable device; e.g., 90% or 4% transmissivity.Alternatively, the ending optical state may be an intermediate opticalstate having a value somewhere between the maximum and minimum opticalstates for the optically switchable device; e.g., 50% transmissivity.

“Bus bar” refers to an electrically conductive strip attached to aconductive layer such as a transparent conductive electrode spanning thearea of an optically switchable device. The bus bar delivers electricalpotential and current from an external lead to the conductive layer. Anoptically switchable device includes two or more bus bars, eachconnected to a single conductive layer of the device. In variousembodiments, a bus bar forms a long thin line that spans most of thelength of the length or width of a device. Often, a bus bar is locatednear the edge of the device.

“Applied Voltage” or V_(app) refers the difference in potential appliedto two bus bars of opposite polarity on the electrochromic device. Eachbus bar is electronically connected to a separate transparent conductivelayer. The applied voltage may different magnitudes or functions such asdriving an optical transition or holding an optical state. Between thetransparent conductive layers are sandwiched the optically switchabledevice materials such as electrochromic materials. Each of thetransparent conductive layers experiences a potential drop between theposition where a bus bar is connected to it and a location remote fromthe bus bar. Generally, the greater the distance from the bus bar, thegreater the potential drop in a transparent conducting layer. The localpotential of the transparent conductive layers is often referred toherein as the V_(TCL). Bus bars of opposite polarity may be laterallyseparated from one another across the face of an optically switchabledevice.

“Effective Voltage” or V_(eff) refers to the potential between thepositive and negative transparent conducting layers at any particularlocation on the optically switchable device. In Cartesian space, theeffective voltage is defined for a particular x,y coordinate on thedevice. At the point where V_(eff) is measured, the two transparentconducting layers are separated in the z-direction (by the devicematerials), but share the same x,y coordinate.

“Hold Voltage” refers to the applied voltage necessary to indefinitelymaintain the device in an ending optical state. In some cases, withoutapplication of a hold voltage, electrochromic windows return to theirnatural tint state. In other words, maintenance of a desired tint staterequires application of a hold voltage.

“Drive Voltage” refers to the applied voltage provided during at least aportion of the optical transition. The drive voltage may be viewed as“driving” at least a portion of the optical transition. Its magnitude isdifferent from that of the applied voltage immediately prior to thestart of the optical transition. In certain embodiments, the magnitudeof the drive voltage is greater than the magnitude of the hold voltage.An example application of drive and hold voltages is depicted in FIG. 3

Context and Overview

The disclosed embodiments make use of electrical probing and monitoringto evaluate an unknown optical state (e.g., tint state or other opticalcharacteristic) of an optically switchable device and/or to determinewhen an optical transition between a first optical state and a secondoptical state of an optically switchable device has proceeded to asufficient extent that the application of a drive voltage can beterminated. For example, electrical probing allows for application ofdrive voltages for less time than previously thought possible, as aparticular device is driven based on electrical probing of its actualoptical transition progression in real time. Further, real timemonitoring can help ensure that an optical transition progresses to adesired state. The electrical probing and monitoring techniquesdescribed herein can also be used to monitor/control optical transitionsthat begin during the course of a previously ongoing optical transition.A number of different control techniques are available, with certaintechniques being especially well suited for accomplishing differenttypes of tasks as described further below.

In various embodiments, terminating the drive voltage is accomplished bydropping the applied voltage to a hold voltage. This approach takesadvantage of an aspect of optical transitions that is typicallyconsidered undesirable—the propensity of thin optically switchabledevices to transition between optical states non-uniformly. Inparticular, many optically switchable devices initially transition atlocations close to the bus bars and only later at regions far from thebus bars (e.g., near the center of the device). Surprisingly, thisnon-uniformity can be harnessed to probe the optical transition. Byallowing the transition to be probed in the manner described herein,optically switchable devices avoid the need for custom characterizationand associated preprogramming of device control algorithms specifyingthe length of time a drive voltage is applied as well as obviating “onesize fits all” fixed time period drive parameters that account forvariations in temperature, device structure variability, and the likeacross many devices. Further, the probing techniques can also be used todetermine the optical state (e.g., tint state) of an opticallyswitchable device having an unknown optical state, making suchtechniques useful both before and during an optical transition. Beforedescribing probing and monitoring techniques in more detail, somecontext on optical transitions in electrochromic devices will beprovided.

Driving a transition in a typical electrochromic device is accomplishedby applying a defined voltage to two separated bus bars on the device.In such a device, it is convenient to position bus bars perpendicular tothe smaller dimension of a rectangular window (see FIG. 1A). This isbecause the transparent conducting layers used to deliver an appliedvoltage over the face of the thin film device have an associated sheetresistance, and the bus bar arrangement allows for the shortest spanover which current must travel to cover the entire area of the device,thus lowering the time it takes for the conductor layers to be fullycharged across their respective areas, and thus lowering the time totransition the device.

While an applied voltage, V_(app), is supplied across the bus bars,essentially all areas of the device see a lower local effective voltage(V_(eff)) due to the sheet resistance of the transparent conductinglayers and the current draw of the device. The center of the device (theposition midway between the two bus bars) frequently has the lowestvalue of V_(eff). This may result in an unacceptably small opticalswitching range and/or an unacceptably slow switching time in the centerof the device. These problems may not exist at the edges of the device,nearer the bus bars. This is explained in more detail below withreference to FIGS. 1B and 1C.

FIG. 1A shows a top-down view of an electrochromic lite 100 includingbus bars having a planar configuration. Electrochromic lite 100 includesa first bus bar 105 disposed on a first conductive layer 110 and asecond bus bar 115 disposed on a second conductive layer, 120. Anelectrochromic stack (not shown) is sandwiched between first conductivelayer 110 and second conductive layer 120. As shown, first bus bar 105may extend substantially across one side of first conductive layer 110.Second bus bar 115 may extend substantially across one side of secondconductive layer 120 opposite the side of electrochromic lite 100 onwhich first bus bar 105 is disposed. Some devices may have extra busbars, e.g. on all four edges, but this complicates fabrication. Afurther discussion of bus bar configurations, including planarconfigured bus bars, is found in U.S. patent application Ser. No.13/452,032 filed Apr. 20, 2012, which is incorporated herein byreference in its entirety.

FIG. 1B is a graph showing a plot of the local voltage in firsttransparent conductive layer 110 and the voltage in second transparentconductive layer 120 that drives the transition of electrochromic lite100 from a clear state to a tinted state, for example. Plot 125 showsthe local values of the voltage V_(TCL) in first transparent conductivelayer 110. As shown, the voltage drops from the left hand side (e.g.,where first bus bar 105 is disposed on first conductive layer 110 andwhere the voltage is applied) to the right hand side of first conductivelayer 110 due to the sheet resistance and current passing through firstconductive layer 110. Plot 130 also shows the local voltage V_(TCL) insecond conductive layer 120. As shown, the voltage increases (decreasesin magnitude) from the right hand side (e.g., where second bus bar 115is disposed on second conductive layer 120 and where the voltage isapplied) to the left hand side of second conductive layer 120 due to thesheet resistance of second conductive layer 120. The value of theapplied voltage, V_(app), in this example is the difference in voltagebetween the right end of potential plot 130 and the left end ofpotential plot 125. The value of the effective voltage, V_(eff), at anylocation between the bus bars is the difference in values of curves 130and 125 at the position on the x-axis corresponding to the location ofinterest.

FIG. 1C is a graph showing a plot of V_(eff) across the electrochromicdevice between first and second conductive layers 110 and 120 ofelectrochromic lite 100. As explained, the effective voltage is thelocal voltage difference between the first conductive layer 110 and thesecond conductive layer 120. Regions of an electrochromic devicesubjected to higher effective voltages transition between optical statesfaster than regions subjected to lower effective voltages. As shown, theeffective voltage is the lowest at the center of electrochromic lite 100and highest at the edges of electrochromic lite 100. The voltage dropacross the device is due to ohmic losses as current passes through thedevice. The voltage drop across large electrochromic windows can bealleviated by configuring additional bus bars within the viewing area ofthe window, in effect dividing one large optical window into multiplesmaller electrochromic windows which can be driven in series orparallel. However, this approach may not be aesthetically appealing dueto the contrast between the viewable area and the bus bar(s) in theviewable area. That is, it may be much more pleasing to the eye to havea monolithic electrochromic device without any distracting bus bars inthe viewable area.

As described above, as the window size increases, the electronicresistance to current flowing across the thin face of the TC layers alsoincreases. This resistance may be measured between the points closest tothe bus bar (referred to as edge of the device in following description)and in the points furthest away from the bus bars (referred to as thecenter of the device in following description). When current passesthrough a TCL, the voltage drops across the TCL face and this reducesthe effective voltage at the center of the device. This effect isexacerbated by the fact that typically as window area increases, theleakage current density for the window stays constant but the totalleakage current increases due to the increased area. Thus with both ofthese effects the effective voltage at the center of the electrochromicwindow falls substantially, and poor performance may be observed forelectrochromic windows which are larger than, for example, about 30inches across. This issue can be addressed by using a higher V_(app)such that the center of the device reaches a suitable effective voltage.

Typically the range of safe operation for solid state electrochromicdevices is between about 0.5V and 4V, or more typically between about0.8V and about 3V, e.g. between 0.9V and 1.8V. These are local values ofV_(eff). In one embodiment, an electrochromic device controller orcontrol algorithm provides a driving profile where V_(eff) is alwaysbelow 3V, in another embodiment, the controller controls V_(eff) so thatit is always below 2.5V, in another embodiment, the controller controlsV_(eff) so that it is always below 1.8V. The recited voltage valuesrefer to the time averaged voltage (where the averaging time is of theorder of time required for small optical response, e.g. few seconds tofew minutes).

An added complexity of electrochromic windows is that the current drawnthrough the window is not fixed over the duration of the opticaltransition. Instead, during the initial part of the transition, thecurrent through the device is substantially larger (up to 100× larger)than in the end state when the optical transition is complete or nearlycomplete. The problem of poor coloration in center of the device isfurther exacerbated during this initial transition period, as the valueV_(eff) at the center is significantly lower than what it will be at theend of the transition period.

In the case of an electrochromic device with a planar bus bar, it can beshown that the V_(eff) across a device with planar bus bars is generallygiven by:

ΔV(0)=V _(app) −RJL ²/2

ΔV(L)=V _(app) −RJL ²/2

ΔV(L/2)=V _(app)−3RJL ²/4  Equation 1

where:V_(app) is the voltage difference applied to the bus bars to drive theelectrochromic window;ΔV(0) is V_(eff) at the bus bar connected to the first transparentconducting layer (in the example below, TEC type TCO);ΔV(L) is V_(eff) at the bus bar connected to the second transparentconducting layer (in the example below, ITO type TCO);ΔV(L/2) is V_(eff) at the center of the device, midway between the twoplanar bus bars;R=transparent conducting layer sheet resistance;J=instantaneous average current density; andL=distance between the bus bars of the electrochromic device.

The transparent conducting layers are assumed to have substantiallysimilar, if not the same, sheet resistance for the calculation. Howeverthose of ordinary skill in the art will appreciate that the applicablephysics of the ohmic voltage drop and local effective voltage stillapply even if the transparent conducting layers have dissimilar sheetresistances.

As noted, certain embodiments pertain to controllers and controlalgorithms for driving optical transitions in devices having planar busbars. In such devices, substantially linear bus bars of oppositepolarity are disposed at opposite sides of a rectangular or otherpolygonally shaped electrochromic device. In some embodiments, deviceswith non-planar bus bars may be employed. Such devices may employ, forexample, angled bus bars disposed at vertices of the device. In suchdevices, the bus bar effective separation distance, L, is determinedbased on the geometry of the device and bus bars. A discussion of busbar geometries and separation distances may be found in U.S. patentapplication Ser. No. 13/452,032, entitled “Angled Bus Bar”, and filedApr. 20, 2012, which is incorporated herein by reference in itsentirety.

As R, J or L increase, V_(eff) across the device decreases, therebyslowing or reducing the device coloration during transition and even inthe final optical state. Referring to Equation 1, the V_(eff) across thewindow is at least RJL²/2 lower than V_(app). It has been found that asthe resistive voltage drop increases (due to increase in the windowsize, current draw etc.) some of the loss can be negated by increasingV_(app) but doing so only to a value that keeps V_(eff) at the edges ofthe device below the threshold where reliability degradation wouldoccur.

In summary, it has been recognized that both transparent conductinglayers experience ohmic drop, and that drop increases with distance fromthe associated bus bar, and therefore V_(TCL) decreases with distancefrom the bus bar for both transparent conductive layers. As aconsequence V_(eff) decreases in locations removed from both bus bars.

To speed along optical transitions, the applied voltage is initiallyprovided at a magnitude greater than that required to hold the device ata particular optical state in equilibrium. This approach is illustratedin FIGS. 2 and 3.

FIG. 2 shows a complete current profile and voltage profile for anelectrochromic device employing a simple voltage control algorithm tocause an optical state transition cycle (tinting followed by clearing)of an electrochromic device. In the graph, total current density (I) isrepresented as a function of time. As mentioned, the total currentdensity is a combination of the ionic current density associated with anelectrochromic transition and electronic leakage current between theelectrochemically active electrodes. Many different types ofelectrochomic devices will have the depicted current profile. In oneexample, a cathodic electrochromic material such as tungsten oxide isused in conjunction with an anodic electrochromic material such asnickel tungsten oxide in counter electrode. In such devices, negativecurrents indicate coloration/tinting of the device. In one example,lithium ions flow from a nickel tungsten oxide anodically coloringelectrochromic electrode into a tungsten oxide cathodically coloringelectrochromic electrode. Correspondingly, electrons flow into thetungsten oxide electrode to compensate for the positively chargedincoming lithium ions. Therefore, the voltage and current are shown tohave a negative value.

The depicted profile results from ramping up the voltage to a set leveland then holding the voltage to maintain the optical state. The currentpeaks 201 are associated with changes in optical state, i.e., tintingand clearing. Specifically, the current peaks represent delivery of theionic charge needed to tint or clear the device. Mathematically, theshaded area under the peak represents the total charge required to tintor clear the device. The portions of the curve after the initial currentspikes (portions 203) represent electronic leakage current while thedevice is in the new optical state.

In the figure, a voltage profile 205 is superimposed on the currentcurve. The voltage profile follows the sequence: negative ramp (207),negative hold (209), positive ramp (211), and positive hold (213). Notethat the voltage remains constant after reaching its maximum magnitudeand during the length of time that the device remains in its definedoptical state. Voltage ramp 207 drives the device to its new the tintedstate and voltage hold 209 maintains the device in the tinted stateuntil voltage ramp 211 in the opposite direction drives the transitionfrom tinted to clear states. In some switching algorithms, a current capis imposed. That is, the current is not permitted to exceed a definedlevel in order to prevent damaging the device (e.g. driving ion movementthrough the material layers too quickly can physically damage thematerial layers). The coloration speed is a function of not only theapplied voltage, but also the temperature and the voltage ramping rate.

FIG. 3 illustrates a voltage control profile in accordance with certainembodiments. In the depicted embodiment, a voltage control profile isemployed to drive the transition from a clear state to a tinted state(or to an intermediate state). To drive an electrochromic device in thereverse direction, from a tinted state to a clear state (or from a moretinted to less tinted state), a similar but inverted profile is used. Insome embodiments, the voltage control profile for going from tinted toclear is a mirror image of the one depicted in FIG. 3.

The voltage values depicted in FIG. 3 represent the applied voltage(V_(app)) values. The applied voltage profile is shown by the dashedline. For contrast, the current density in the device is shown by thesolid line. In the depicted profile, V_(app) includes four components: aramp to drive component 303, which initiates the transition, a V_(drive)component 313, which continues to drive the transition, a ramp to holdcomponent 315, and a V_(hold) component 317. The ramp components areimplemented as variations in V_(app) and the V_(drive) and V_(hold)components provide constant or substantially constant V_(app)magnitudes.

The ramp to drive component is characterized by a ramp rate (increasingmagnitude) and a magnitude of V_(drive). When the magnitude of theapplied voltage reaches V_(drive), the ramp to drive component iscompleted. The V_(drive) component is characterized by the value ofV_(drive) as well as the duration of V_(drive). The magnitude ofV_(drive) may be chosen to maintain V_(eff) with a safe but effectiverange over the entire face of the electrochromic device as describedabove.

The ramp to hold component is characterized by a voltage ramp rate(decreasing magnitude) and the value of V_(hold) (or optionally thedifference between V_(drive) and V_(hold)). V_(app) drops according tothe ramp rate until the value of V_(hold) is reached. The V_(hold)component is characterized by the magnitude of V_(hold) and the durationof V_(hold). Actually, the duration of V_(hold) is typically governed bythe length of time that the device is held in the tinted state (orconversely in the clear state). Unlike the ramp to drive, V_(drive), andramp to hold components, the V_(hold) component has an arbitrary length,which is independent of the physics of the optical transition of thedevice.

Each type of electrochromic device will have its own characteristiccomponents of the voltage profile for driving the optical transition.For example, a relatively large device and/or one with a more resistiveconductive layer will require a higher value of V_(drive) and possibly ahigher ramp rate in the ramp to drive component. U.S. patent applicationSer. No. 13/449,251, filed Apr. 17, 2012, and incorporated herein byreference, discloses controllers and associated algorithms for drivingoptical transitions over a wide range of conditions. As explainedtherein, each of the components of an applied voltage profile (ramp todrive, V_(drive), ramp to hold, and V_(hold), herein) may beindependently controlled to address real-time conditions such as currenttemperature, current level of transmissivity, etc. In some embodiments,the values of each component of the applied voltage profile is set for aparticular electrochromic device (having its own bus bar separation,resistivity, etc.) and does not vary based on current conditions. Inother words, in such embodiments, the voltage profile does not take intoaccount feedback such as temperature, current density, and the like.

As indicated, all voltage values shown in the voltage transition profileof FIG. 3 correspond to the V_(app) values described above. They do notcorrespond to the V_(eff) values described above. In other words, thevoltage values depicted in FIG. 3 are representative of the voltagedifference between the bus bars of opposite polarity on theelectrochromic device.

In certain embodiments, the ramp to drive component of the voltageprofile is chosen to safely but rapidly induce ionic current to flowbetween the electrochromic and counter electrodes. As shown in FIG. 3,the current in the device follows the profile of the ramp to drivevoltage component until the ramp to drive portion of the profile endsand the V_(drive) portion begins. See current component 301 in FIG. 3.Safe levels of current and voltage can be determined empirically orbased on other feedback. U.S. Pat. No. 8,254,013, filed Mar. 16, 2011,issued Aug. 28, 2012 and incorporated herein by reference, presentsexamples of algorithms for maintaining safe current levels duringelectrochromic device transitions.

In certain embodiments, the value of V_(drive) is chosen based on theconsiderations described above. Particularly, it is chosen so that thevalue of V_(eff) over the entire surface of the electrochromic deviceremains within a range that effectively and safely transitions largeelectrochromic devices. The duration of V_(drive) can be chosen based onvarious considerations. One of these ensures that the drive potential isheld for a period sufficient to cause the substantial coloration of thedevice. For this purpose, the duration of V_(drive) may be determinedempirically, by monitoring the optical density of the device as afunction of the length of time that V_(drive) remains in place. In someembodiments, the duration of V_(drive) is set to a specified timeperiod. In another embodiment, the duration of V_(drive) is set tocorrespond to a desired amount of ionic and/or electronic charge beingpassed. As shown, the current ramps down during V_(drive). See currentsegment 307.

Another consideration is the reduction in current density in the deviceas the ionic current decays as a consequence of the available lithiumions completing their journey from the anodic coloring electrode to thecathodic coloring electrode (or counter electrode) during the opticaltransition. When the transition is complete, the only current flowingacross device is leakage current through the ion conducting layer. As aconsequence, the ohmic drop in potential across the face of the devicedecreases and the local values of V_(eff) increase. These increasedvalues of V_(eff) can damage or degrade the device if the appliedvoltage is not reduced. Thus, another consideration in determining theduration of V_(drive) is the goal of reducing the level of V_(eff)associated with leakage current. By dropping the applied voltage fromV_(drive) to V_(hold), not only is V_(eff) reduced on the face of thedevice but leakage current decreases as well. As shown in FIG. 3, thedevice current transitions in a segment 305 during the ramp to holdcomponent. The current settles to a stable leakage current 309 duringV_(hold).

Controlling V_(drive) Using Feedback from the Optical Transition

A challenge arises because it can be difficult to predict an optimumvalue for V_(drive), and/or how long the applied drive voltage should beapplied before transitioning to the hold voltage. Devices of differentsizes, and more particularly devices having bus bars separated byparticular distances, require different optimal drive voltages anddifferent lengths of time for applying the drive voltage. Further, theprocesses employed to fabricate optically switchable devices such aselectrochromic devices may vary subtly from one batch to another or oneprocess revision to another. The subtle process variations translateinto potentially different requirements for the optimal drive voltageand length of time that the drive voltage must be applied to the devicesused in operation. Still further, environmental conditions, andparticularly temperature, can influence the length of time that theapplied voltage should be applied to drive the transition.

To account for all these variables, current technology may define manydistinct control algorithms with distinct periods of time for applying adefined drive voltage for each of many different window sizes or devicefeatures. A rationale for doing this is to ensure that the drive voltageis applied for a sufficient period, regardless of device size and type,to ensure that the optical transition is complete. Currently manydifferent sized electrochromic windows are manufactured. While it ispossible to pre-determine the appropriate drive voltage time for eachand every different type of window, this can be a tedious, expensive,and time-consuming process. An improved approach, described here, is todetermine on-the-fly the length of time that the drive voltage should beapplied.

Further, it may be desirable to cause the transition between two definedoptical states to occur within a defined duration, regardless of thesize of the optically switchable device, the process under which thedevice is fabricated, and the environmental conditions in which thedevice is operating at the time of the transition. This goal can berealized by monitoring the course of the transition and adjusting thedrive voltage as necessary to ensure that the transition completes inthe defined time. Adjusting the magnitude of the drive voltage is oneway of accomplishing this.

In a number of embodiments, a probing technique may be used to evaluatethe optical state of an optically switchable device. Often, the opticalstate relates to the tint state of the device, though other opticalproperties may be probed in certain implementations. The optical stateof the device may or may not be known prior to the initiation of anoptical transition. In some cases, a controller may have informationabout the current optical state of the device. In other cases, acontroller may not have any such information available. Therefore, inorder to determine an appropriate drive algorithm, it may be beneficialto probe the device in a manner that allows for determination of thedevice's current optical state before beginning any new drivealgorithms. For example, if the device is in a fully tinted state, itmay damage the device to send various voltages and/or polarities throughthe device. By knowing the current state of the device, the risk ofsending any such damaging voltages and/or polarities through the devicecan be minimized, and appropriate drive algorithms can be employed.

In various embodiments, an unknown optical state may be determined byapplying open circuit conditions to the optically switchable device, andmonitoring the open circuit voltage (V_(oc)). This technique isparticularly useful for determining the tint state of an electrochromicdevice, though it may also be used in some cases where a differentoptical characteristic is being determined and/or cases where adifferent type of optically switchable device is used. In manyembodiments, the optical state of an optically switchable device is adefined function of V_(oc). As a result, V_(oc) can be measured todetermine the optical state of the device. This determination allows forthe drive algorithm to be tailored to the particular optical transitionthat is to occur (e.g., from the determined starting optical state tothe desired ending optical state). This technique is particularly usefuland accurate when the device has been quiescent (i.e., not activelytransitioning) for a period of time (e.g., about 1-30 minutes or longer)before the measurement takes place. In some cases, temperature may alsobe taken into account when determining the optical state of the devicebased on the measured V_(oc). However, in various embodiments therelationship between optical state and V_(oc) varies little withtemperature, and as such, temperature may be ignored when determiningthe optical state based on the measured V_(oc).

Certain disclosed embodiments apply a probing technique to assess theprogress of an optical transition while the device is in transition. Asillustrated in FIG. 3, there are typically distinct ramp to drive andthe drive voltage maintenance stages of the optical transition. Theprobe technique can be applied during either of these. In manyembodiments, it is applied during the drive voltage maintenance portionof the algorithm.

In certain embodiments, the probing technique involves pulsing thecurrent or voltage applied to drive the transition and then monitoringthe current or voltage response to detect an overdrive condition in thevicinity of the bus bars. An overdrive condition occurs when the localeffective voltage is greater than needed to cause a local opticaltransition. For example, if an optical transition to a clear state isdeemed complete when V_(eff) reaches 2V, and the local value of V_(eff)near a bus bar is 2.2V, the position near the bus bar may becharacterized as in an overdrive condition.

One example of a probing technique involves pulsing the applied drivevoltage by dropping it to the level of the hold voltage (or the holdvoltage modified by an appropriate offset) and monitoring the currentresponse to determine the direction of the current response. In thisexample, when the current response reaches a defined threshold, thedevice control system determines that it is now time to transition fromthe drive voltage to the hold voltage. Another example of a probingtechnique mentioned above involves applying open circuit conditions tothe device and monitoring the open circuit voltage, V_(oc). This may bedone to determine the optical state of an optical device and/or tomonitor/control an optical transition. Further, in a number of cases,the amount of charge passed to the optically switchable device (orrelatedly, the delivered charge or charge density) may be monitored andused to control an optical transition.

FIG. 4A is a graph depicting an optical transition in which a drop inapplied voltage from V_(drive) to V_(hold) results in a net current flowestablishing that the optical transition has proceeded far enough topermit the applied voltage to remain at V_(hold) for the duration of theending optical state. This is illustrated by a voltage drop 411 inV_(app) from V_(drive) to V_(hold). Voltage drop 411 is performed duringa period when the V_(app) might otherwise be constrained to remain inthe drive phase shown in FIG. 3. The current flowing between the busbars began dropping (becoming less negative), as illustrated by currentsegment 307, when the applied voltage initially stopped increasing(becoming more negative) and plateaued at V_(drive). However, when theapplied voltage now dropped at 411, the current began decreasing morereadily as illustrated by current segment 415. In accordance with someembodiments, the level of current is measured after a defined period oftime passes following the voltage drop 411. If the current is below acertain threshold, the optical transition is deemed complete, and theapplied voltage may remain at V_(hold) (or move to V_(hold) if it is atsome other level below V_(drive)). In the particular example of FIG. 4A,the current threshold is exceeded as illustrated. Therefore, the V_(app)remains at V_(hold) for the duration of the ending optical state.V_(hold) may be selected for the ending optical state it provides. Suchending optical state may be a maximum, minimum, or intermediate opticalstate for the optical device undergoing the transition.

In situations where the current does not reach the threshold whenmeasured, it may be appropriate to return V_(app) to V_(drive). FIG. 4Billustrates this situation. FIG. 4B is a graph depicting an opticaltransition in which an initial drop in applied voltage from V_(drive) toV_(hold) (see 411) results in a net current flow indicating that theoptical transition has not yet proceeded far enough to permit theapplied voltage to remain at V_(hold) for the duration of the endingoptical state. Note that current segment 415, which has a trajectoryresulting from voltage drop 411, does not reach the threshold whenprobed at 419. Therefore the applied voltage is returned to V_(drive)for a further period of time—while the current recovers at 417—beforeagain dropping again to V_(hold) (421) at which point the resultingcurrent (423) establishes that the optical transition has proceeded farenough to permit the applied voltage to remain at V_(hold) for theduration of the ending optical state. As explained, the ending opticalstate may be a maximum, minimum, or intermediate optical state for theoptical device undergoing the transition.

As explained, the hold voltage is a voltage that will maintain theoptical device in equilibrium at a particular optical density or otheroptical condition. It produces a steady-state result by generating acurrent that offsets the leakage current in the ending optical state.The drive voltage is applied to speed the transition to a point whereapplying the hold voltage will result in a time invariant desiredoptical state.

Certain probing techniques described herein may be understood in termsof the physical mechanisms associated with an optical transition drivenfrom bus bars at the edges of a device. Basically, such techniques relyon differential values of the effective voltage experienced in theoptically switchable device across the face of the device, andparticularly the variation in V_(eff) from the center of the device tothe edge of the device. The local variation in potential on thetransparent conductive layers results in different values of V_(eff)across the face of the device. The value of V_(eff) experienced by theoptically switchable device near the bus bars is far greater the valueof V_(eff) in the center of the device. As a consequence, the localcharge buildup in the region next to the bus bars is significantlygreater than the charge buildup in the center the device.

At some point during the optical transition, the value of V_(eff) at theedge of the device near the bus bars is sufficient to exceed the endingoptical state desired for the optical transition whereas in the centerof the device, the value of V_(eff) is insufficient to reach that endingstate. The ending state may be an optical density value associated withthe endpoint in the optical transition. While in this intermediate stageof the optical transition, if the drive voltage is dropped to the holdvoltage, the portion of the electrochromic device close to the bus barswill effectively try to transition back toward the state from which itstarted. However, as the device state in the center of the device hasnot yet reached the end state of the optical transition, when a holdvoltage is applied, the center portion of the device will continuetransitioning in the direction desired for the optical transition.

When the device in this intermediate stage of transition experiences thechange in applied voltage from the drive voltage to the hold voltage (orsome other suitably lower magnitude voltage), the portions of the devicelocated near the bus bars—where the device is effectivelyoverdriven—generate current flowing in the direction opposite thatrequired to drive the transition. In contrast, the regions of the devicein the center, which have not yet fully transitioned to the final state,continue to promote current flow in a direction required to drive thetransition.

Over the course of the optical transition, and while the device isexperiencing the applied drive voltage, there is a gradual increase inthe driving force for causing current to flow in the reverse directionwhen the device is subject to a sudden drop in applied voltage. Bymonitoring the flow of current in response to perturbations away fromdrive voltage, one can determine a point at which the transition fromthe first state to the second state is sufficiently far along that atransition from drive voltage to hold voltage is appropriate. By“appropriate,” it is meant that the optical transition is sufficientlycomplete from the edge of the device to the center of the device. Suchtransition can be defined in many ways depending upon the specificationsof the product and its application. In one embodiment, it assumes thatthe transition from the first state to the second state is at leastabout 80% of complete or at least about 95% of complete. Completereflecting the change in optical density from the first state to thesecond state. The desired level of completeness may correspond to athreshold current level as depicted in the examples of FIGS. 4A and 4B.

Many possible variations to the probing protocol exist. Such variationsmay include certain pulse protocols defined in terms of the length oftime from the initiation of the transition to the first pulse, theduration of the pulses, the size of the pulses, and the frequency of thepulses.

In one embodiment, the pulse sequence is begun immediately upon theapplication of a drive voltage or a ramp to drive voltage that initiatesthe transition between the first optical state and second optical state.In other words, there would be no lag time between the initiation of thetransition and the application of pulsing. In some implementations, theprobe duration is sufficiently short (e.g., about 1 second or less) thatprobing back and forth between V_(drive) and V_(hold) for the entiretransition is not significantly detrimental to switching time. However,in some embodiments, it is unnecessary to start probing right away. Insome cases, switching is initiated after about 50% of an expected ornominal switching period is complete, or about 75% of such period iscomplete. Often, the distance between bus bars is known or can be readusing an appropriately configured controller. With the distance known, aconservative lower limit for initiating probing may be implemented basedon approximate known switching time. As an example, the controller maybe configured to initiate probing after about 50-75% of expectedswitching duration is complete.

In some embodiments, the probing begins after about 30 seconds frominitiating the optical transition. Relatively earlier probing may beespecially helpful in cases where an interrupt command is received. Aninterrupt command is one that instructs the device to switch to a thirdoptical transmission state when the device is already in the process ofchanging from a first to a second optical transmission state). In thiscase, early probing can help determine the direction of the transition(i.e, whether the interrupt command requires the window to becomelighter or darker than when the command is received). In someembodiments, the probing begins about 120 minutes (e.g., about 30minutes, about 60 minutes, or about 90 minutes) after initiating theoptical transition. Relatively later probing may be more useful wherelarger windows are used, and where the transition occurs from anequilibrium state. For architectural glass, probing may begin about 30seconds to 30 minutes after initiating the optical transition, in somecases between about 1-5 minutes, for example between about 1-3 minutes,or between about 10-30 minutes, or between about 20-30 minutes. In someembodiments, the probing begins about 1-5 minutes (e.g., about 1-3minutes, about 2 minutes in a particular example) after initiating anoptical transition through an interrupt command, while the probingbegins about 10-30 minutes (e.g., about 20-30 minutes) after initiatingan optical transition from an initial command given when theelectrochromic device is in an equilibrium state.

In the examples of FIGS. 4A and 4B, the size of the pulses is betweenthe drive voltage value and the hold voltage value. This may be done forconvenience. Other pulse magnitudes are possible. For example, the pulsemay a magnitude of about +/− about 500 mV of the hold voltage, or about+/−200 mV of the hold voltage. For context, an electrochromic device ona window, such as an architectural window, may have a drive voltage ofabout 0 volts to +/−20 volts (e.g., about +/−2 volts to +/−10 volts) anda hold voltage of about 0 volts to +/−4 volts (e.g., about +/−1 volt to+/−2 volts).

In various embodiments, the controller determines when during theoptical transition the polarity of the probe current opposes thepolarity of the bias due to transition proceeding to a significantextent. In other words, the current to the bus bars flows in a directionopposite of what would be expected if the optical transition was stillproceeding.

Probing by dropping the applied voltage magnitude from V_(drive) toV_(hold) provides a convenient, and broadly applicable, mechanism formonitoring the transition to determine when the probe current firstreverses polarity. Probing by dropping the voltage to a magnitude otherthan that of V_(hold) may involve characterization of windowperformance. It appears that even very large windows (e.g., about 60″)essentially complete their optical transition when the current firstopposes the transition upon probing from V_(drive) to V_(hold).

In certain cases, probing occurs by dropping the applied voltagemagnitude from V_(drive) to V_(probe), where V_(probe) is a probevoltage other than the hold voltage. For example, V_(probe) may beV_(hold) as modified by an offset. Although many windows are able toessentially complete their optical transitions when the current firstopposes the transition after probing from V_(drive) to V_(hold), certainwindows may benefit from pulsing to a voltage slightly offset from thehold voltage. In general, the offset becomes increasingly beneficial asthe size of the window increases, and as the temperature of the windowdrops. In certain cases, the offset is between about 0-1V, and themagnitude of V_(probe) is between about 0-1V higher than the magnitudeof V_(hold). For example, the offset may be between about 0-0.4V. Inthese or other embodiments, the offset may be at least about 0.025V, orat least about 0.05V, or at least about 0.1V. The offset may result inthe transition having a longer duration than it otherwise would. Thelonger duration helps ensure that the optical transition is able tofully complete. Techniques for selecting an appropriate offset from thehold voltage are discussed further below in the context of a target opencircuit voltage.

In some embodiments, the controller notifies a user or the windownetwork master controller of how far (by, e.g., percentage) the opticaltransition has progressed. This may be an indication of whattransmission level the center of the window is currently at. Feedbackregarding transition may be provided to user interface in a mobiledevice or other computational apparatus. See e.g., PCT PatentApplication No. US2013/036456 filed Apr. 12, 2013, which is incorporatedherein by reference in its entirety.

The frequency of the probe pulsing may be between about 10 seconds and500 seconds. As used in this context, the “frequency” means theseparation time between the midpoints of adjacent pulses in a sequenceof two or more pulses. Typically, the frequency of the pulsing isbetween about 10 seconds and 120 seconds. In certain embodiments, thefrequency the pulsing is between about 20 seconds and 30 seconds. Incertain embodiments, the probe frequency is influenced by the size ofthe electrochromic device or the separation between bus bars in thedevice. In certain embodiments, the probe frequency is chosen as afunction the expected duration of the optical transition. For example,the frequency may be set to be about ⅕^(th) to about 1/50^(th) (or about1/10^(th) to about 1/30^(th)) of the expected duration of the transitiontime. Note that transition time may correspond to the expected durationof V_(app)=V_(drive). Note also that the expected duration of thetransition may be a function of the size of the electrochromic device(or separation of bus bars). In one example, the duration for 14″windows is ˜2.5 minutes, while the duration for 60″ windows is −40minutes. In one example, the probe frequency is every 6.5 seconds for a14″ window and every 2 minutes for a 60″ window.

In various implementations, the duration of each pulse is between about1×10⁵ and 20 seconds. In some embodiments, the duration of the pulses isbetween about 0.1 and 20 seconds, for example between about 0.5 secondsand 5 seconds.

As indicated, in certain embodiments, an advantage of the probingtechniques disclosed herein is that only very little information need bepre-set with the controller that is responsible for controlling a windowtransition. Typically, such information includes only the hold voltage(and voltage offset, if applicable) associated for each optical endstate. Additionally, the controller may specify a difference in voltagebetween the hold voltage and a drive voltage, or alternatively, thevalue of V_(drive) itself. Therefore, for any chosen ending opticalstate, the controller would know the magnitudes of V_(hold), V_(offset)and V_(drive). The duration of the drive voltage is determined using theprobing algorithm described here. In other words, the controllerdetermines how to appropriately apply the drive voltage as a consequenceof actively probing the extent of the transition in real time.

FIG. 5A presents a flowchart 501 for a process of monitoring andcontrolling an optical transition in accordance with certain disclosedembodiments. As depicted, the process begins with an operation denotedby reference number 503, where a controller or other control logicreceives instructions to direct the optical transition. As explained,the optical transition may be an optical transition between a tintedstate and a more clear state of electrochromic device. The instructionsfor directing the optical transition may be provided to the controllerbased upon a preprogrammed schedule, an algorithm reacting to externalconditions, manual input from a user, etc. Regardless of how theinstructions originate, the controller acts on them by applying a drivevoltage to the bus bars of the optically switchable device. See theoperation denoted by reference number 505.

As explained above, in conventional embodiments, the drive voltage isapplied to the bus bars for a defined period of time after which it ispresumed that the optical transition is sufficiently complete that theapplied voltage can be dropped to a hold voltage. In such embodiments,the hold voltage is then maintained for the duration of the pendingoptical state. In contrast, in accordance with embodiments disclosedherein, the transition from a starting optical state to an endingoptical state is controlled by probing the condition of the opticallyswitchable device one or more times during the transition. Thisprocedure is reflected in operations 507, et seq. of FIG. 5A.

In operation 507, the magnitude of the applied voltage is dropped afterallowing the optical transition to proceed for an incremental period oftime. The duration of this incremental transition is significantly lessthan the total duration required to fully complete the opticaltransition. Upon dropping the magnitude of the applied voltage, thecontroller measures the response of the current flowing to the bus bars.See operation 509. The relevant controller logic may then determinewhether the current response indicates that the optical transition isnearly complete. See decision 511. As explained above, the determinationof whether an optical transition is nearly complete can be accomplishedin various ways. For example, it may be determined by the currentreaching a particular threshold. Assuming that the current response doesnot indicate that the optical transition is nearly complete, processcontrol is directed to an operation denoted by reference number 513. Inthis operation, the applied voltage is returned to the magnitude of thedrive voltage. Process controls then loops back to operation 507 wherethe optical transition is allowed to proceed by a further incrementbefore again dropping the magnitude of the applied voltage to the busbars.

At some point in the procedure 501, decision operation 511 determinesthat the current response indicates that the optical transition is infact nearly complete. At this point, process control proceeds to anoperation indicated by reference number 515, where the applied voltageis transitioned to or maintained at the hold voltage for the duration ofthe ending optical state. At this point, the process is complete.

Separately, in some implementations, the method or controller mayspecify a total duration of the transition. In such implementations, thecontroller may be programmed to use a modified probing algorithm tomonitor the progress of the transition from the starting state to theend state. The progress can be monitored by periodically reading acurrent value in response to a drop in the applied voltage magnitudesuch as with the probing technique described above. The probingtechnique may also be implemented using a drop in applied current (e.g.,measuring the open circuit voltage) as explained below. The current orvoltage response indicates how close to completion the opticaltransition has come. In some cases, the response is compared to athreshold current or voltage for a particular time (e.g., the time thathas elapsed since the optical transition was initiated). In someembodiments, the comparison is made for a progression of the current orvoltage responses using sequential pulses or checks. The steepness ofthe progression may indicate when the end state is likely to be reached.A linear extension to this threshold current may be used to predict whenthe transition will be complete, or more precisely when it will besufficiently complete that it is appropriate to drop the drive voltageto the hold voltage.

With regard to algorithms for ensuring that the optical transition fromfirst state to the second state occurs within a defined timeframe, thecontroller may be configured or designed to increase the drive voltageas appropriate to speed up the transition when the interpretation of thepulse responses suggests that the transition is not progressing fastenough to meet the desired speed of transition. In certain embodiments,when it is determined that the transition is not progressingsufficiently fast, the transition switches to a mode where it is drivenby an applied current. The current is sufficiently great to increase thespeed of the transition but is not so great that it degrades or damagesthe electrochromic device. In some implementations, the maximum suitablysafe current may be referred to as I_(safe). Examples of I_(safe) mayrange between about 5 and 250 μA/cm². In current controlled drive mode,the applied voltage is allowed to float during the optical transition.Then, during this current controlled drive step, could the controllerperiodically probes by, e.g., dropping to the hold voltage and checkingfor completeness of transition in the same way as when using a constantdrive voltage.

In general, the probing technique may determine whether the opticaltransition is progressing as expected. If the technique determines thatthe optical transition is proceeding too slowly, it can take steps tospeed the transition. For example, it can increase the drive voltage.Similarly, the technique may determine that the optical transition isproceeding too quickly and risks damaging the device. When suchdetermination is made, the probing technique may take steps to slow thetransition. As an example, the controller may reduce the drive voltage.

In some applications, groups of windows are set to matching transitionrates. The windows in the group may or may not start from the samestarting optical state, and may or may not end at the same endingoptical state. In certain embodiments, the windows will start from thesame, first, optical state and transition to the same, second,transition state. In one embodiment, the matching is accomplished byadjusting the voltage and/or driving current based on the feedbackobtained during the probing described herein (by pulse or open circuitmeasurements). In embodiments where the transition is controlled bymonitoring the current response, the magnitude of the current responseand/or an accumulation of charge delivered to the optically switchabledevice may be compared from controller to controller (for each of thegroup of windows) to determine how to scale the driving potential ordriving current for each window in the group. The rate of change of opencircuit voltage could be used in the same manner. In another embodiment,a faster transitioning window may utilize one or more pauses in order toswitch over the same duration as a slower switching window, as describedbelow in relation to FIG. 5K. The pauses may correspond to preset tintstates, or not.

FIG. 5B presents a flowchart 521 depicting an example process forensuring that the optical transition occurs sufficiently fast, e.g.,within a defined time period. The first four depicted operations inflowchart 521 correspond to the first four operations in flowchart 501.In other words, operation 523, 525, 527, and 529 of flowchart 521correspond to operations 503, 505, 507, and 509 of flowchart 501.Briefly, in operation 523, the controller or other appropriate logicreceives instructions to undergo an optical transition. Then, atoperation 525, the controller applies a drive voltage to the bus bars.After allowing the optical transition to proceed incrementally, thecontroller drops the magnitude of the applied voltage to the bus bars.See operation 527. The magnitude of the lower voltage is typically,though not necessarily, the hold voltage. As mentioned, the lowervoltage may also be the hold voltage as modified by an offset (theoffset often falling between about 0-1V, for example between about0-0.4V in many cases). Next, the controller measures the currentresponse to the applied voltage drop. See operation 529.

The controller next determines whether the current response indicatesthat the optical transition is proceeding too slowly. See decision 531.As explained, the current response may be analyzed in various waysdetermine whether the transition is proceeding with sufficient speed.For example, the magnitude of the current response may be considered orthe progression of multiple current responses to multiple voltage pulsesmay be analyzed to make this determination.

Assuming that operation 531 establishes that the optical transition isproceeding rapidly enough, the controller then increases the appliedvoltage back to the drive voltage. See operation 533. Thereafter, thecontroller then determines whether the optical transition issufficiently complete that further progress checks are unnecessary. Seeoperation 535. In certain embodiments, the determination in operation535 is made by considering the magnitude of the current response asdiscussed in the context of FIG. 5A. Assuming that the opticaltransition is not yet sufficiently complete, process control returns tooperation 527, where the controller allows the optical transition toprogress incrementally further before again dropping the magnitude ofthe applied voltage.

Assuming that execution of operation 531 indicates that the opticaltransition is proceeding too slowly, process control is directed to anoperation 537 where the controller increases the magnitude of theapplied voltage to a level that is greater than the drive voltage. Thisover drives the transition and hopefully speeds it along to a level thatmeets specifications. After increasing the applied voltage to thislevel, process control is directed to operation 527 where the opticaltransition continues for a further increment before the magnitude of theapplied voltage is dropped. The overall process then continues throughoperation 529, 531, etc. as described above. At some point, decision 535is answered in the affirmative and the process is complete. In otherwords, no further progress checks are required. The optical transitionthen completes as illustrated in, for example, flowchart 501.

Another application of the probing techniques disclosed herein involveson-the-fly modification of the optical transition to a different endstate. In some cases, it will be necessary to change the end state aftera transition begins. Examples of reasons for such modification include auser's manual override a previously specified end tint state and a widespread electrical power shortage or disruption. In such situations, theinitially set end state might be transmissivity=40% and the modified endstate might be transmissivity=5%.

Where an end state modification occurs during an optical transition, theprobing techniques disclosed herein can adapt and move directly to thenew end state, rather than first completing the transition to theinitial end state.

In some implementations, the transition controller/method detects thecurrent state of the window using a voltage/current sense as disclosedherein and then moves to a new drive voltage immediately. The new drivevoltage may be determined based on the new end state and optionally thetime allotted to complete the transition. If necessary, the drivevoltage is increased significantly to speed the transition or drive agreater transition in optical state. The appropriate modification isaccomplished without waiting for the initially defined transition tocomplete. The probing techniques disclosed herein provide a way todetect where in the transition the device is and make adjustments fromthere.

It should be understood that the probing techniques presented hereinneed not be limited to measuring the magnitude of the device's currentin response to a voltage drop (pulse). There are various alternatives tomeasuring the magnitude of the current response to a voltage pulse as anindicator of how far as the optical transition has progressed. In oneexample, the profile of a current transient provides useful information.In another example, measuring the open circuit voltage of the device mayprovide the requisite information. In such embodiments, the pulseinvolves simply applying no voltage to device and then measuring thevoltage that the open circuit device applies. Further, it should beunderstood that current and voltage based algorithms are equivalent. Ina current based algorithm, the probe is implemented by dropping theapplied current and monitoring the device response. The response may bea measured change in voltage. For example, the device may be held in anopen circuit condition to measure the voltage between bus bars.

FIG. 5C presents a flowchart 501 for a process of monitoring andcontrolling an optical transition in accordance with certain disclosedembodiments. In this case, the process condition probed is the opencircuit voltage, as described in the previous paragraph. The first twodepicted operations in flowchart 541 correspond to the first twooperations in flowcharts 501 and 521. In other words, operations 543 and545 of flowchart 541 correspond to operations 503 and 505 of flowchart501. Briefly, in operation 543, the controller or other appropriatelogic receives instructions to undergo an optical transition. Then, atoperation 545, the controller applies a drive voltage to the bus bars.After allowing the optical transition to proceed incrementally, thecontroller applies open circuit conditions to the electrochromic deviceat operation 547. Next, the controller measures the open circuit voltageresponse at operation 549.

As is the case above, the controller may measure the electronic response(in this case the open circuit voltage) after a defined period haspassed since applying the open circuit conditions. Upon application ofopen circuit conditions, the voltage typically experiences an initialdrop relating to the ohmic losses in external components connected tothe electrochromic device. Such external components may be, for example,conductors and connections to the device. After this initial drop, thevoltage experiences a first relaxation and settles at a first plateauvoltage. The first relaxation relates to internal ohmic losses, forexample over the electrode/electrolyte interfaces within theelectrochromic devices. The voltage at the first plateau corresponds tothe voltage of the cell, with both the equilibrium voltage and theovervoltages of each electrode. After the first voltage plateau, thevoltage experiences a second relaxation to an equilibrium voltage. Thissecond relaxation is much slower, for example on the order of hours. Insome cases it is desirable to measure the open circuit voltage duringthe first plateau, when the voltage is relatively constant for a shortperiod of time. This technique may be beneficial in providing especiallyreliable open circuit voltage readings. In other cases, the open circuitvoltage is measured at some point during the second relaxation. Thistechnique may be beneficial in providing sufficiently reliable opencircuit readings while using less expensive and quick-operatingpower/control equipment.

In some embodiments, the open circuit voltage is measured after a setperiod of time after the open circuit conditions are applied. Theoptimal time period for measuring the open circuit voltage is dependentupon the distance between the bus bars. The set period of time mayrelate to a time at which the voltage of a typical or particular deviceis within the first plateau region described above. In such embodiments,the set period of time may be on the order of milliseconds (e.g., a fewmilliseconds in some examples). In other cases, the set period of timemay relate to a time at which the voltage of a typical or particulardevice is experiencing the second relaxation described above. Here, theset period of time may be on the order of about 1 second to severalseconds, in some cases. Shorter times may also be used depending on theavailable power supply and controller. As noted above, the longer times(e.g., where the open circuit voltage is measured during the secondrelaxation) may be beneficial in that they still provide useful opencircuit voltage information without the need for high end equipmentcapable of operating precisely at very short timeframes.

In certain implementations, the open circuit voltage ismeasured/recorded after a timeframe that is dependent upon the behaviorof the open circuit voltage. In other words, the open circuit voltagemay be measured over time after open circuit conditions are applied, andthe voltage chosen for analysis may be selected based on the voltage vs.time behavior. As described above, after application of open circuitconditions, the voltage goes through an initial drop, followed by afirst relaxation, a first plateau, and a second relaxation. Each ofthese periods may be identified on a voltage vs. time plot based on theslope of curve. For example, the first plateau region will relate to aportion of the plot where the magnitude of dV_(oc)/dt is relatively low.This may correspond to conditions in which the ionic current has stopped(or nearly stopped) decaying. As such, in certain embodiments, the opencircuit voltage used in the feedback/analysis is the voltage measured ata time when the magnitude of dV_(oc)/dt drops below a certain threshold.

Returning to FIG. 5C, after the open circuit voltage response ismeasured, it can be compared to a target open circuit voltage atoperation 551. The target open circuit voltage may correspond to thehold voltage. In certain cases, discussed further below, the target opencircuit voltage corresponds to the hold voltage as modified by anoffset. Techniques for choosing an appropriate offset from the holdvoltage are discussed further below. Where the open circuit voltageresponse indicates that the optical transition is not yet nearlycomplete (i.e., where the open circuit voltage has not yet reached thetarget open circuit voltage), the method continues at operation 553,where the applied voltage is increased to the drive voltage for anadditional period of time. After the additional period of time haselapsed, the method can repeat from operation 547, where the opencircuit conditions are again applied to the device. At some point in themethod 541, it will be determined in operation 551 that the open circuitvoltage response indicates that the optical transition is nearlycomplete (i.e., where the open circuit voltage response has reached thetarget open circuit voltage). When this is the case, the methodcontinues at operation 555, where the applied voltage is transitioned toor maintained at the hold voltage for the duration of the ending opticalstate.

The method 541 of FIG. 5C is very similar to the method 501 of FIG. 5A.The main difference is that in FIG. 5C, the relevant variable measuredis the open circuit voltage, while in FIG. 5A, the relevant variablemeasured is the current response when a reduced voltage is applied. Inanother embodiment, the method 521 of FIG. 5B is modified in the sameway. In other words, the method 521 may be altered such that probingoccurs by placing the device in open circuit conditions and measuringthe open circuit voltage rather than a current response.

In another embodiment, the process for monitoring and controlling anoptical transition takes into account the total amount of chargedelivered to the electrochromic device during the transition, per unitarea of the device. This quantity may be referred to as the deliveredcharge or charge density, or total delivered charge or charge density.As such, an additional criterion such as the total charge or chargedensity delivered may be used to ensure that the device fullytransitions under all conditions.

The total delivered charge or charge density may be compared to athreshold charge or threshold charge density (also referred to as atarget charge or charge density) to determine whether the opticaltransition is nearly complete. The threshold charge or threshold chargedensity may be chosen based on the minimum charge or charge densityrequired to fully complete or nearly complete the optical transitionunder the likely operating conditions. In various cases, the thresholdcharge or threshold charge density may be chosen/estimated based on thecharge or charge density required to fully complete or nearly completethe optical transition at a defined temperature (e.g., at about −40° C.,at about −30° C., at about −20° C., at about −10° C., at about 0° C., atabout 10° C., at about 20° C., at about 25° C., at about 30° C., atabout 40° C., at about 60° C., etc.).

A suitable threshold charge or threshold charge density may also beaffected by the leakage current of the electrochromic device. Devicesthat have higher leakage currents should have higher threshold chargedensities. In some embodiments, an appropriate threshold charge orthreshold charge density may be determined empirically for an individualwindow or window design. In other cases, an appropriate threshold may becalculated/selected based on the characteristics of the window such asthe size, bus bar separation distance, leakage current, starting andending optical states, etc. Example threshold charge densities rangebetween about 1×10⁻⁵ C/cm² and about 5 C/cm², for example between about1×10⁻⁴ and about 0.5 C/cm², or between about 0.005-0.05 C/cm², orbetween about 0.01-0.04 C/cm², or between about 0.01-0.02 in many cases.Smaller threshold charge densities may be used for partial transitions(e.g., fully clear to 25% tinted) and larger threshold charge densitiesmay be used for full transitions. A first threshold charge or chargedensity may be used for bleaching/clearing transitions, and a secondthreshold charge or charge density may be used for coloring/tintingtransitions. In certain embodiments, the threshold charge or chargedensity is higher for tinting transitions than for clearing transitions.In a particular example, the threshold charge density for tinting isbetween about 0.013-0.017 C/cm², and the threshold charge density forclearing is between about 0.016-0.020 C/cm². Additional threshold chargedensities may be appropriate where the window is capable oftransitioning between more than two states. For instance, if the deviceswitches between four different optical states: A, B, C, and D, adifferent threshold charge or charge density may be used for eachtransition (e.g., A to B, A to C, A to D, B to A, etc.).

In some embodiments, the threshold charge or threshold charge density isdetermined empirically. For instance, the amount of charge required toaccomplish a particular transition between desired end states may becharacterized for devices of different sizes. A curve may be fit foreach transition to correlate the bus bar separation distance with therequired charge or charge density. Such information may be used todetermine the minimum threshold charge or threshold charge densityrequired for a particular transition on a given window. In some cases,the information gathered in such empirical determinations is used tocalculate an amount of charge or charge density that corresponds to acertain level of change (increase or decrease) in optical density.

FIG. 5D presents a flow chart for a method 561 for monitoring andcontrolling an optical transition in an electrochromic device. Themethod starts at operations 563 and 565, which correspond to operations503 and 505 of FIG. 5A. At 563, the controller or other appropriatelogic receives instructions to undergo an optical transition. Then, atoperation 565, the controller applies a drive voltage to the bus bars.After allowing the optical transition to proceed incrementally, themagnitude of the voltage applied to the bus bars is reduced to a probevoltage (which in some cases is the hold voltage, and in other cases isthe hold voltage modified by an offset) at operation 567. Next atoperation 569, the current response to the reduced applied voltage ismeasured.

Thus far, the method 561 of FIG. 5D is identical to the method 501 ofFIG. 5A. However, the two methods diverge at this point in the process,with method 561 continuing at operation 570, where the total deliveredcharge or charge density is determined. The total delivered charge orcharge density may be calculated based on the current delivered to thedevice during the optical transition, integrated over time. At operation571, the relevant controller logic may determine whether the currentresponse and total delivered charge or charge density each indicate thatthe optical transition is nearly complete. As explained above, thedetermination of whether an optical transition is nearly complete can beaccomplished in various ways. For example, it may be determined by thecurrent reaching a particular threshold, and by the delivered charge orcharge density reaching a particular threshold. Both the currentresponse and the total delivered charge or charge density must indicatethat the transition is nearly complete before the method can continue onat operation 575, where the applied voltage is transitioned to ormaintained at the hold voltage for the duration of the ending opticalstate. Assuming at least one of the current response and total deliveredcharge or charge density indicate that the optical transition is not yetnearly complete at operation 571, process control is directed to anoperation denoted by reference number 573. In this operation, theapplied voltage is returned to the magnitude of the drive voltage.Process control then loops back to operation 567 where the opticaltransition is allowed to proceed by a further increment before againdropping the magnitude of the applied voltage to the bus bars.

FIG. 5E presents an alternative method for monitoring and controlling anoptical transition in an electrochromic device. The method starts atoperations 583 and 585, which correspond to operations 503 and 505 ofFIG. 5A. At 583, the controller or other appropriate logic receivesinstructions to undergo an optical transition. Then, at operation 585,the controller applies a drive voltage to the bus bars. After allowingthe optical transition to proceed incrementally, open circuit conditionsare applied to the device at operation 587. Next at operation 589, theopen circuit voltage of the device is measured.

Thus far, the method 581 of FIG. 5E is identical to the method 541 ofFIG. 5C. However, the two methods diverge at this point in the process,with method 581 continuing at operation 590, where the total deliveredcharge or charge density is determined. The total delivered charge orcharge density may be calculated based on the current delivered to thedevice during the optical transition, integrated over time. At operation591, the relevant controller logic may determine whether the opencircuit voltage and total delivered charge or charge density eachindicate that the optical transition is nearly complete. Both the opencircuit voltage response and the total delivered charge or chargedensity must indicate that the transition is nearly complete before themethod can continue on at operation 595, where the applied voltage istransitioned to or maintained at the hold voltage for the duration ofthe ending optical state. Assuming at least one of the open circuitvoltage response and total delivered charge or charge density indicatethat the optical transition is not yet nearly complete at operation 591,process control is directed to an operation denoted by reference number593. In this operation, the applied voltage is returned to the magnitudeof the drive voltage. Process control then loops back to operation 587where the optical transition is allowed to proceed by a furtherincrement before again applying open circuit conditions to the device.The method 581 of FIG. 5E is very similar to the method 561 of FIG. 5D.The principal difference between the two embodiments is that in FIG. 5D,the applied voltage drops and a current response is measured, whereas inFIG. 5E, open circuit conditions are applied and an open circuit voltageis measured.

FIG. 5F illustrates a flowchart for a related method 508 for controllingan optical transition in an electrochromic device. The method 508 ofFIG. 5F is similar to the method 581 of FIG. 5E. The method 508 beginsat operation 510 where the controller is turned on. Next, at operation512, the open circuit voltage (V_(oc)) is read and the device waits foran initial command. By measuring V_(oc), the current optical state ofthe device can be determined, as described above. Because this opticalstate is the starting optical state for a transition to the next state,it can be beneficial to characterize this state before sending newcommands to the device, thereby minimizing the risk of damaging thedevice. An initial command is received at operation 514, the commandindicating that the window should switch to a different optical state.After the command is received, open circuit conditions are applied andthe open circuit voltage is measured at operation 516. The amount ofcharge delivered (Q) may also be read at block 516. These parametersdetermine the direction of the transition (whether the window issupposed to get more tinted or more clear), and impact the optimal driveparameter. An appropriate drive parameter (e.g., drive voltage) isselected at operation 516. This operation may also involve revising thetarget charge count and target open circuit voltage, particularly incases where an interrupt command is received, as discussed furtherbelow.

After the open circuit voltage is read at operation 516, theelectrochromic device is driven for a period of time. The drive durationmay be based on the busbar separation distance in some cases. In othercases, a fixed drive duration may be used, for example about 30 seconds.This driving operation may involve applying a drive voltage or currentto the device. Operation 518 may also involve modifying a driveparameter based on the sensed open circuit voltage and/or charge count.Next, at operation 520, it is determined whether the total time of thetransition (thus far) is less than a threshold time. Example thresholdtimes may be about 1 hour, about 2 hours, about 3 hours, about 4 hours,and any range between these examples, though other time periods may beused as appropriate. If it is determined that the total time oftransition is not less than the threshold time (e.g., where thetransition has taken at least 2 hours and is not yet complete), thecontroller may indicate that it is in a fault state at operation 530.This may indicate that something has caused an error in the transitionprocess. Otherwise, where the total time of transition is determined tobe less than the threshold time, the method continues at operation 522.Here, open circuit conditions are again applied, and the open circuitvoltage is measured. At operation 524, it is determined whether themeasured open circuit voltage is greater than or equal to the targetvoltage (in terms of magnitude). If so, the method continues atoperation 526, where it is determined whether the charge count (Q) isgreater than or equal to the target charge count. If the answer ineither of operations 524 or 526 is no, the method returns to block 518where the electrochromic device transition is driven for an additionaldrive duration. Where the answer in both of operations 524 and 526 isyes, the method continues at operation 528, where a hold voltage isapplied to maintain the electrochromic device in the desired tint state.Typically, the hold voltage continues to be applied until a new commandis received, or until a timeout is experienced.

When a new command is received after the transition is complete, themethod may return to operation 516. Another event that can cause themethod to return to operation 516 is receiving an interrupt command, asindicated in operation 532. An interrupt command may be received at anypoint in the method after an initial command is received at operation514 and before the transition is essentially complete at operation 528.The controller should be capable of receiving multiple interruptcommands over a transition. One example interrupt command involves auser directing a window to change from a first tint state (e.g., fullyclear) to a second tint state (e.g., fully tinted), then interruptingthe transition before the second tint state is reached to direct thewindow to change to a third tint state (e.g., half tinted) instead ofthe second tint state. After receiving a new command or an interruptcommand, the method returns to block 516 as indicated above. Here, opencircuit conditions are applied and the open circuit voltage and chargecount are read. Based on the open circuit voltage and charge countreadings, as well as the desired third/final tint state, the controlleris able to determine appropriate drive conditions (e.g., drive voltage,target voltage, target charge count, etc.) for reaching the third tintstate. For instance, the open circuit voltage/charge count may be usedto indicate in which direction the transition should occur. The chargecount and charge target may also be reset after receiving a new commandor an interrupt command. The updated charge count may relate to thecharge delivered to move from the tint state when the new/interruptcommand is received to the desired third tint state. Because the newcommand/interrupt command will change the starting and ending points ofthe transition, the target open circuit voltage and target charge countmay need to be revised. This is indicated as an optional part ofoperation 516, and is particularly relevant where a new or interruptcommand is received.

FIGS. 5G and 5H together describe an embodiment where an opticallyswitchable device is controlled using a number of different modesdepending on the type of task the device is undertaking. Three differentmodes of operation will be discussed with reference to these figures. Ina first mode a controller associated with the window measures V_(oc) butdoes not monitor the amount of charge delivered to the device. In asecond mode, the controller associated with the window measures V_(oc)and monitors the amount of charge delivered to the device. In a thirdmode, the controller associated with the window monitors the amount ofcharge delivered to the device, but does not measure V_(oc). The firstmode is especially useful for controlling transitions from an unknownstate (e.g., after power loss, first bootup) to a known end state. Insome cases, an optically switchable device may default to this mode ofoperation after power loss or any case when the initial state of thewindow is unknown. The second mode is especially useful for controllingtransitions between a known starting optical state and a known endingoptical state. This mode may be used any time there is a transitionbetween two known states that is uninterrupted. The third mode ofoperation may be especially useful for controlling optical transitionsthat begin during a previously ongoing optical transition (e.g., when aninterrupt command is received). When an ongoing transition isinterrupted in this way, the third mode may provide superior controlover the transition compared to the other modes.

Returning to FIGS. 5G and 5H, it is noted that FIG. 5H presentsoperation 552 of FIG. 5G in greater detail. The method 540 begins withoperation 542 where an initial command is received. The initial commandinstructs the device to change to a particular ending optical state,referred to in FIG. 5G as end state 1. Next, open circuit conditions areapplied and the open circuit voltage (V_(oc)) is measured in operation544. Measuring V_(oc) allows for the optical state of the device to bedetermined. This optical state corresponds to the starting optical statefor the optical transition. During operation 544, the window isoperating in the first mode mentioned above. Next, the initial driveparameter(s) are determined in operation 546. The drive parameters maybe determined based, at least in part, on end state 1 and the startingoptical state determined in operation 544. Often, the drive parametersrelate to a voltage or current applied to the device, sometimes referredto as the drive voltage and drive current, respectively. At operation548, the drive parameter(s) are applied to the device for a period oftime and the optical transition begins.

Next, it is determined whether an interrupt command has been received inoperation 550. In some cases this may be actively checked, while inother cases this determination may be made passively (e.g., thewindow/controller may not actively check whether a command has beenreceived, but rather, the window/controller may take action with respectto the interrupt command when such a command has been received, i.e.,the controller/window may automatically respond to an interruptcommand). An interrupt command is one that is received while a previousoptical transition is ongoing, and directs the device to undergo atransition to a state other than end state 1. An interrupt command maybe used to cause the device to transition to a different ending opticalstate, referred to as end state 2. End state 2 may be more or lesstinted than end state 1 (where the optically switchable device is anelectrochromic device, for example). In a simple case, end state 2 maybe the starting optical state, in which case the interrupt commandessentially cancels the ongoing transition and causes the device toreturn to its starting optical state.

In the example of FIGS. 5G and 5H, the previous ongoing transition isthe transition to end state 1 from the starting optical state determinedin operation 544. The interrupt command instructs the device to insteadundergo a second transition, this time to end state 2. Where aninterrupt command has been received, the method 540 continues withoperation 552, where the device transitions to end state 2. Operation552 is explained in further detail in FIG. 5H.

In cases where no interrupt command has been received in operation 550,the method 540 continues at operation 554. Here, the device may beprobed to evaluate how far along the optical transition has progressed.In this example, operation 554 involves applying open circuit conditionsand measuring the open circuit voltage (V_(oc)). This operation alsoinvolves monitoring the amount of charge delivered to the device,referred to as the Q_(count). The total delivered charge or chargedensity may be monitored in some cases. At operation 556, it isdetermined whether V_(oc) has reached V_(target). This typicallyinvolves comparing the magnitude of V_(oc) to the magnitude ofV_(target). The value of V_(oc) may increase or decrease over time,depending on the transition. As such, the term “reach” (for example asused in relation to V_(oc) reaching V_(target)) may mean that themagnitude of V_(oc) should reach a value that is equal to or greaterthan the magnitude of V_(target), or that the magnitude of V_(oc) shouldreach a value that is equal to or less than the magnitude of V_(target).Those of ordinary skill in the art understand how to determine whichcondition to use based on the transition that is occurring. If themagnitude of V_(oc) reaches the magnitude of the target voltage, themethod continues with operation 558, where the charge delivered to thedevice (the Q_(count) is compared to target charge count (Q_(target)).If the amount of charge delivered to the device reaches or exceedsQ_(target), the optical transition is complete and the device hasreached end state 1, at which point a hold voltage may be applied asshown in operation 560.

In cases where the magnitude of V_(oc) has not reached V_(target) inoperation 556, and/or where the Q_(count) has not reached Q_(target) inoperation 558, the method instead continues at operation 548, where thedrive parameter(s) are applied to the device to drive the opticaltransition for an additional duration. During operations 546, 548, 550,554, 556, and 558 (particularly 554, 556, and 558), thewindow/controller may be understood to be operating in the second modementioned above (where both V_(oc) and charge count are taken intoaccount).

Turning to FIG. 5H, operation 552 (transition device to end state 2) maybe undertaken using a number of steps, as shown. At operation 562, whiletransitioning to end state 1, an interrupt command is received thatindicates that the device should instead transition to end state 2.Based on this command, the window/controller may switch into aparticular mode of operation, such as the third mode described abovewhere the feedback for controlling the transition is based primarily onthe amount of charge delivered to the device. At operation 576, it isdetermined how much charge has been delivered to the device (Q_(count))during the transition from the starting state toward end state 1. ThisQ_(count) indicates how far along the first transition had proceeded,and also provides an indication/estimate of what the current opticalstate of the window is likely to be. Next, at operation 564, a secondQ_(target) is determined based on end state 2. This second Q_(target)may correlate to an amount of charge that would be appropriate fordelivering to the device to cause the device to transition from thestarting optical state (before the transition toward end state 1) to endstate 2. In such cases, the Q_(count) may be counted cumulatively fromthe beginning of the first transition toward end state 1, all the waythrough the transition to end state 2. In a similar embodiment, thesecond Q_(target) may correlate to an amount of charge that would beappropriate for delivering to the device to cause the device totransition from its instantaneous optical state (e.g., the optical stateat the point in time when the interrupt command is received in operation562) to end state 2. In these cases, the Q_(count) may be reset at thetime when the interrupt command is received. In some such cases, theinstantaneous optical state of the device may be inferred based on theQ_(count) delivered while transitioning toward end state 1. For thepurpose of FIG. 5H, it is assumed that the first method is used andQ_(count) is measured cumulatively from the beginning of the firsttransition toward end state 1.

Next, at operation 566, updated drive parameter(s) are determined fordriving the device toward end state 2. In particular, the polarity andmagnitude of the drive parameter(s) may be determined, for example adrive voltage or drive current. The updated drive parameter(s) may bedetermined based on the second Q_(target) and the Q_(count) deliveredduring the transition from the starting state toward end state 1. Inother words, the updated drive parameter(s) are determined based on thenew target optical state (end state 2) and how far along the firsttransition was before it was interrupted. These determinations arefurther described with reference to FIG. 5I, described below. Atoperation 568, the updated drive parameter(s) are applied to the deviceand the optical transition toward end state 2 is driven for a period oftime. During this operation, the amount of charge delivered to thedevice (Q_(count)) may be monitored, either continuously orperiodically. At operation 572, it is determined whether the Q_(count)has reached the second Q_(target). This determination depends, at leastin part, on whether or not the optical transition changed direction as aresult of the interrupt command, as explained further in relation toFIG. 5I. Where the Q_(count) has not reached the second Q_(target), themethod returns to operation 568, where the drive parameter(s) areapplied and the device is driven toward end state 2 for an additionalduration. Once the Q_(count) reaches the second Q_(target), the secondoptical transition is complete, and a hold voltage may be applied tomaintain end state 2.

Various steps presented in FIGS. 5G and 5H (as well as other flowchartsherein) may be done at a different point in time compared to what isshown in the figures. This is particularly true when severalmeasurements and/or determinations are made at once. In such instances,the relevant operations may be done in any available order.

FIG. 5I presents a number of graphs describing aspects of severaloptical transitions for a single optically switchable device, includingtransitions that occur as a result of an interrupt command. The topmostcurve depicts the % Transmission through the electrochromic window atthe center of the device over time. Four different optical states,Tint₁-Tint₄, are labeled on the x-axis, each corresponding to adifferent tint level. Tint₁ is the least tinted state and Tint₄ is themost tinted state. The second curve depicts Q_(count) and Q_(target)over time. The third curve depicts V_(oc) and V_(target) (the targetopen circuit voltage) over time. The fourth and bottommost curve depictsthe set point voltage over time.

At time T₁, a command to undergo a first optical transition is receivedand the device begins to transition to this end state. In this example,the electrochromic device has a starting optical state of Tint₁ at timeT₁. Further, the command received at time T₁ instructs the device tochange to end state 1, which corresponds to Tint₄. In response to thecommand received at time T₁, the window/controller determines aQ_(target) and a V_(target) appropriate for transitioning from thestarting state to end state 1 (from Tint₁ to Tint₄). The transition maybe probed and monitored as described herein, for example by applyingopen circuit conditions, measuring the V_(oc), and comparing toV_(target), as well as by monitoring the charge delivered to the device(Q_(count)) and comparing it to Q_(target). However, before this opticaltransition is complete, a second command is received at time T₂. Thecommand received at T₂ instructs the window to undergo a differentoptical transition (referred to herein as the second optical transition)to a different end state, end state 2, which corresponds to Tint₃. Inother words, at time T₂, it is determined that instead of transitioningall the way to end state 1, Tint₄, the window should instead transitionto a lesser degree of tint, to end state 2, Tint₃.

At time T₂ when this command is made, the device is at an instantaneousoptical state of Tint₂. Because the instantaneous optical state of thewindow at time T₂ is between the starting optical state and end state 2(between Tint₁ and Tint₃), the optical transition will continue in thesame direction (i.e., the polarity of the drive parameter(s) will be thesame as used during the transition toward end state 1 at Tint₄). Also attime T₂, the target open circuit voltage (V_(target)) becomes irrelevantfor the duration of the optical transition to end state 2 at Tint₃. Thetarget open circuit voltage is no longer considered because at thispoint, the window/controller is operating under the third mode describedabove, which primarily takes into account the charge delivered to thedevice, and not the open circuit voltage. FIG. 5I shows the target opencircuit voltage returning to 0 at time T₂, though it should beunderstood that V_(oc) and V_(target) are simply not being consideredduring the subsequent time period (until a new command is received attime T₃, that is).

As explained in relation to operation 564 in FIG. 5H, a secondQ_(target) is determined at time T₂, with the second Q_(target) beingthe amount of charge appropriate for transitioning from the startingoptical state (Tint₁) to end state 2 (Tint₃). As shown in the plot ofQ&Q_(target) vs. time in FIG. 5I, the magnitude of the second Q_(target)is significantly lower than the magnitude of the first Q_(target), sincethe device is not transitioning as completely when going to end state 2(Tint₃) vs. end state 1 (Tint₄). This optical transition then proceedsuntil the Q_(count) reaches the second Q_(target), at which point thesecond optical transition is complete and a hold voltage may be appliedto maintain the device at end state 2 (Tint₃).

Next, at time T₃, a command is received directing the device to undergoanother optical transition (referred to herein as the third opticaltransition). This command instructs the window to switch to a new endstate, end state 3, at Tint₁. The drive parameters, as well as thetarget open circuit voltage (V_(target)) and target charge count(Q_(target)), may be determined as described herein, for example basedon the starting optical state of the device (Tint₃) and the endingoptical state of the device, end state 3 (Tint₁). This transition may beprobed/monitored as described herein, for example by measuring V_(oc)and comparing to V_(target), and by monitoring Q_(count) and comparingto Q_(target). The third optical transition completes without receivingany interrupt commands. Thus, this transition is deemed to be completeonce V_(oc) reaches V_(target), and once Q_(count) reaches Q_(target).

Then, at time T₄ a new command is received directing the device toundergo another optical transition (referred to herein as the fourthoptical transition). For this transition, the starting optical state isTint₁, and the ending optical state, end state 4, is at Tint₄. Becausethis transition is between the same starting and ending states as thefirst optical transition, the same drive parameters, V_(target), andQ_(target) may be used. The optical transition may be probed/monitoredas described herein, for example by monitoring V_(oc) and comparing toV_(target) and by monitoring Q_(count) and comparing to Q_(target).

Before the fourth optical transition is complete, a new command isreceived at time T₅ directing the device to undergo a different opticaltransition (referred to herein as the fifth optical transition) to adifferent end state, end state 5 at Tint₃. The command received at timeT₅, like the one received at time T₂, is an interrupt command (since itdirects the device to undergo a different optical transition while aprevious optical transition is still occurring). Based on this newcommand at T₅, a new Q_(target) can be determined as described above.Similarly, V_(target) may be ignored and V_(oc) may not be measured forthe duration of the fifth optical transition, as described above withreference to the second optical transition.

The interrupt command received at T₅ affects the control method slightlydifferently than the interrupt command received at T₂ because the fourthoptical transition was substantially further along at time T₅ than thesecond optical transition was at time T₂. At time T₅, the device hasalready gone past end state 5 (Tint₃). In other words, the instantaneousoptical state of the device, when the interrupt command was received,was not between the starting optical state (Tint₁) and the new desiredending state, end state 5 (Tint₃). Whereas the transition keepsoccurring in the same direction at time T₂ (such that the polarity ofthe drive parameters is the same when comparing the first and secondtransitions), the opposite is true at time T₅ (such that the polarity ofthe drive parameters is different when comparing the fourth and fifthtransitions). As shown in the lowermost graph depicting the setpointvoltage, V_(setpoint) changes from negative to positive at time T₅. Bycomparison, at time T₂, the magnitude of V_(setpoint) decreases, but thepolarity remains negative. Similarly, at time T₅ the charge passed tothe device switches directions on the graph, heading up toward 0. Thisswitch happens because current is flowing in the opposite directionwithin the device than was occurring during the fourth opticaltransition.

Because the interrupt command caused a switch in the direction/polaritybetween the fourth and fifth optical transitions, the determination ofwhether the charge delivered to the device (Q_(count)) has reachedQ_(target) is made somewhat differently. Whereas the second opticaltransition is considered complete when the magnitude of the Q_(count) isgreater than or equal to the magnitude of Q_(target), the fifth opticaltransition is considered complete when the magnitude of the Q_(count) isless than or equal to the magnitude of Q_(target). Therefore, as usedherein, the term “reach” (for example as used in relation to determiningwhether the Q_(count) has reached Q_(target)) may mean that themagnitude of Q_(count) should reach a value greater than the magnitudeof Q_(target), or that the magnitude of Q_(count) should reach a valueless than the magnitude of Q_(target). Those of ordinary skill in theart are capable of determining which condition should be used based onwhether the instantaneous optical state of the device at the time theinterrupt command is received is between the starting optical state andthe new desired ending state.

FIG. 5J provides a flowchart for an alternative method 580 forcontrolling an optical transition. The method presented in FIG. 5Jpromotes faster switching times while ensuring that the device isoperated within safe limits. Briefly, the method of FIG. 5J achieves adynamic drive voltage that is selected based on the open circuit voltageand a comparison of the open circuit voltage to the maximum effectivesafe voltage for the device. Many current driving algorithms use presetvoltage drives that are sufficiently low to avoid damaging the device.Such damage typically occurs as a result of overdriving the edges of thedevice. The effective voltage on the device increases over time based onthe drive voltage chosen and the ramp rate used to transition to thedrive voltage. The majority of the time, the device is well below thesafe voltage limit for operation. However, these current drivingalgorithms result in slower-than-optimal switching speeds. Fasterswitching can be attained by driving the device at a drive voltage thatis closer to the safe voltage limit during a greater proportion of theswitch time. However, with such methods, care should be taken to ensurethat the drive voltage does not exceed safe limits for the device.

Improved switching speed can be achieved by using the method 580 shownin FIG. 5J. In this method, the open circuit voltage (V_(oc)) isessentially used as a proxy for the maximum safe effective voltage(V_(safe)). In cases where V_(safe) is known (e.g., through empiricaltesting or other methods available to those of skill in the art), thedrive voltage can be periodically increased until V_(oc) approaches orreaches V_(safe). By operating with V_(oc) at or near the upper limit ofV_(safe), the speed of the optical transition can be maximized whileensuring safe operation. One result of this method is that the magnitudeof the applied voltage is initially high and reduces over time.

The method 580 begins at operation 582 where the drive voltage isapplied to bus bars of the optically switchable device. This drivevoltage may be determined based on the starting optical state and endingoptical state for the optical transition. Next, at operation 584, opencircuit conditions are applied and the open circuit voltage (V_(oc)) ismeasured. Next, at operation 586, it is determined whether V_(oc) hasreached V_(target). V_(target) relates to a target open circuit voltageas described herein. Assuming that this condition is met, the methodcontinues at operation 588, where it is determined whether the amount ofcharge delivered to the device (Q_(count)) has reached the target chargecount for the transition (Q_(target)). Q_(target) may be determined asdescribed herein. Assuming this condition is met, the transition iscomplete and the hold voltage may be applied to maintain the endingoptical state in operation 598. If it is determined that either V_(oc)has not reached V_(target) or that Q_(count) has not reached Q_(target),the transition is not yet complete, and the method continues atoperation 594. Here, the magnitude of V_(oc) is compared to themagnitude of V_(safe). If the magnitude of V_(oc) is greater thanV_(safe), the method continues at operation 596 where the drive voltageis decreased to prevent damage to the device. If the magnitude of V_(oc)is less than V_(safe), the method continues at operation 597 where thedrive voltage is increased. In either case, the drive voltage is appliedfor an additional duration as the method returns to operation 582. Incertain implementations of the method 580, the value used for V_(safe)may include a buffer as described herein to ensure that the drivevoltage never exceeds a value that could result in damage to the device.

FIG. 5K illustrates a flowchart for a method of transitioning aplurality of optically switchable devices, and will be explained in thecontext of the group of optically switchable devices shown in FIG. 10.The method described in FIG. 5K is particularly useful when it isdesired that each optically switchable device in a group of opticallyswitchable devices transitions over approximately the same duration andvisually their tint states approximate each other over the transitionperiod.

Generally speaking, optically switchable devices that are smaller (e.g.,devices that have a smaller bus bar separation distance) transition morequickly than larger optically switchable devices. As used herein, theterms “small,” “large,” and similar descriptors used with respect to thesize of an optically switchable device refer to the distance between thebus bars. In this respect, a 14″×120″ device having a bus bar separationdistance of approximately 14″ is considered smaller than a 20″×20″device having a bus bar separation distance of approximately 20″, eventhough the 20″×20″ device has a larger area.

This difference in switching time is due to sheet resistance intransparent conductor layers within the devices. Given the sametransparent conductor layers with a given sheet resistance, a largerwindow will take more time to switch than a smaller window. In anotherexample, some windows may have improved transparent conductor layers,e.g., having lower sheet resistance than other windows in the group.Methods described herein provide approximate tint state (opticaldensity) matching during transition of a group of windows that havedifferent switching speeds among the group of windows. That is, slowerswitching windows in a group may not necessarily be larger windows. Forthe purposes of this discussion, an example is provided where allwindows of a group of windows have the same optical devicecharacteristics, and thus larger windows switch more slowly than smallerwindows in the group.

With reference to FIG. 10, small optically switchable devices 1090 areexpected to transition more quickly than large optically switchabledevice 1091. Thus, when a group of windows of different sizes transitiontogether, using similar switching algorithms (e.g., similar I/Vparameters), the smaller devices finish transitioning first, while thelarger devices take additional time to transition. This difference inswitching time can be undesirable in certain implementations.

The method 1000 of FIG. 5K starts at operation 1002, where a command isreceived to transition a group of optically switchable devices to anending optical state. In this example, the group includes a large (e.g.,60″) optically switchable device 1091 that transitions relativelyslowly, and several smaller (e.g., 15″) optically switchable devices1090 that transition relatively quickly. In this embodiment, it isdesired that all of the optically switchable devices 1090 and 1091transition over the same time period, for aesthetic purposes. Since thelarger window takes the most time to switch, the switching time for thegroup of windows will be based on the slowest transitioning window inthe group. Operation 1004 therefore involves determining the switchingtime for the slowest transitioning optically switchable device in thegroup. Often, this is the device with the largest bus bar separationdistance. The optical transitions of the faster transitioning devices1090 can be tailored to match the switching time of the slowesttransitioning device 1091. Operation 1004 may be completed whenever agroup or zone of optically switchable devices is defined, where it isexpected that the group or zone of optically switchable devices willtransition together as a group.

In operation 1005, the slowest optically switchable device 1091 istransitioned to the ending optical state. This transition may bemonitored using any of the methods described herein. In some cases,operation 1005 involves repeatedly probing the slowest opticallyswitchable device 1091 during its transition (e.g., using a particularV_(app) and measuring a current response, or applying open circuitconditions and measuring V_(oc), and/or measuring/monitoring an amountof charge or charge density delivered to the optically switchabledevice) to determine when the slowest optically switchable device 1091has reached or is nearing the ending optical state).

Operation 1006 involves transitioning the faster optically switchabledevices 1090 toward the ending optical state, with the objective ofapproximating the tint state of the slower window(s) during transition.Operations 1005 and 1006 typically begin simultaneously (or nearlysimultaneously). Before the faster optically switchable devices 1090reach the ending optical state, the optical transition of the fasteroptically switchable devices 1090 is paused for a duration at operation1008. This pause increases the time it takes for the faster opticallyswitchable devices 1090 to reach the ending optical state. The durationof the pause may be based on the difference in switching times betweenthe faster optically switchable devices 1090 and the slowest opticallyswitchable devices 1091. The tint states of the faster and slowerswitching windows are approximately matched during the transition. Thepause(s) allow the slower switching window to catch up with the fasterswitching windows, e.g., or the pauses are timed and chosen ofsufficient duration such that it appears that the tint states of theslower (in this example, large) and faster (in this example, small)windows display approximately the same optical density throughout thetransition.

After the pause in operation 1008, the method continues with operation1010 where the optical transitions on the faster optically switchabledevices 1090 are resumed such that the faster optically switchabledevices 1090 continue to transition toward the ending optical state.Operations 1008 and 1010 may be repeated any number of times (e.g.,0<n<∞). Generally speaking, using a greater number of pauses will resultin transitions where the different optically switchable devices moreclosely match one another (in terms of optical density at a given time).However, above a certain number of pauses, any additional tint matchingbenefit between the faster switching devices and the slower switchingdevices becomes negligible and there is little or no benefit toincluding additional pauses. In certain embodiments, a faster switchingoptically switchable device may pause 1, 2, 3, 4, 5, or 10 times duringan optical transition in order to match the switching speed of a slowertransitioning optically switchable device. In some cases, a fasterswitching optically switchable device may pause at least twice, or atleast three times, during its transition. In these or other cases, afaster switching optically switchable device may pause a maximum ofabout 20 times, or a maximum of about 10 times, during its transition.The number, duration, and timing of the pauses can be determinedautomatically each time a group of optically switchable devices isdefined, and/or each time a group of optically switchable devices isinstructed to simultaneously undergo a particular transition. Thecalculation may be made based on the characteristics of the opticallyswitchable devices in the group, e.g., the switching time (withoutpauses) for each device in the group, the difference in the switchingtimes for the different devices in the group, the number of devices inthe group, the starting and ending optical states for the transition,the peak power available to the devices in the group, etc. In certainembodiments, determining the number, duration, and/or timing of thepauses may be done using a look-up table based on one or more of thesecriteria.

In one example where the slowest optically switchable device 1091switches in about 35 minutes, the faster optically switchable devices1090 switch in about 5 minutes, and a single pause is used, operation1006 may involve transitioning the faster optically switchable devices1090 for a duration of about 2.5 minutes (e.g., one half of the expectedtransition time for the faster optically switchable devices 1090),operation 1008 may involve pausing the optical transition of the fasteroptically switchable devices 1090 for a duration of about 30 minutes,and operation 1010 may involve continuing to transition the fasteroptically switchable devices 1090 for a duration of about 2.5 minutes.Thus, the total transition time for both the slowest opticallyswitchable device 1091 and for the faster optically switchable devices1090 is 35 minutes. Generally, more pauses are used so as to approximatethe tint state of the larger window(s) during the entire transition ofthe larger window(s).

In another example where the slowest optically switchable device 1091switches in about 35 minutes, the faster optically switchable devices1090 switch in about 5 minutes, and four pauses (e.g., n=4) are usedduring transition of the faster optically switchable devices 1090,operation 1006 and each iteration of operation 1010 may involve drivingthe optical transitions on the faster optically switchable devices 1090for a duration of about 1 minute, and each iteration of operation 1008may involve pausing such transitions for a duration of about 7.5minutes. After the five transition periods at 1 minute each and the fourpauses at 7.5 minutes each, the total transition time for each opticallyswitchable window is 35 minutes.

As described in relation to the slowest optically switchable device 1091in operation 1005, the optical transitions on the faster opticallyswitchable devices 1090 may be monitored using any of the methodsdescribed herein. For instance, operations 1006 and/or 1010 may involverepeatedly probing the faster optically switchable devices 1090 (e.g.,using a particular V_(app) and measuring a current response, or applyingopen circuit conditions and measuring V_(oc), and/ormeasuring/monitoring an amount of charge or charge density delivered tothe optically switchable device) to determine whether the fasteroptically switchable devices 1090 have reached or are nearing the endingoptical state. In some embodiments, the method that is used to monitorthe optical transition on the slowest optically switchable device 1091is the same as the method used to monitor the optical transition on oneor more faster optically switchable devices 1090. In some embodiments,the method used to monitor the optical transition on the slowestoptically switchable device 1091 is different from the method used tomonitor the optical transition on one or more faster opticallyswitchable devices 1090.

Regardless of whether or how the different optical transitions aremonitored, the method continues with operation 1012, where a holdvoltage is applied to each optically switchable device. The hold voltagemay be applied in response to a determination that a relevant opticallyswitchable device has reached or is nearing the ending optical state. Inother cases, the hold voltage may be applied based on known switchingtimes for a particular window or group of windows, without regard to anyfeedback measured during the transitions. The hold voltage may beapplied to each optically switchable device as it reaches or nears theending optical state. The hold voltage may be applied to each opticallyswitchable device at the same time, or within a relatively short periodof time (e.g., within about 1 minute, or within about 5 minutes).

A particular example where feedback is used to monitor the opticaltransitions and determine when to apply the hold voltage to eachoptically switchable device is shown in FIG. 5L. The method 1020 isexplained in the context of the group of windows shown in FIG. 10, whichincludes large optically switchable device 1091 (which is the slowesttransitioning device in the group) and several small opticallyswitchable devices 1090 (which are the faster transitioning devices inthe group). The method 1020 of FIG. 5L shares many features/operationsin common with method 1000 of FIG. 5K. The method 1020 begins withoperation 1002, where a command is received to transition the group ofoptically switchable devices to an ending optical state. Next, atoperation 1004 the switching time for the slowest optically switchabledevice 1091 in the group is determined. This switching time will be thetarget switching time for all the optically switchable devices in thegroup.

At operation 1005, the slowest optically switchable device 1091 istransitioned to the ending optical state. In this embodiment, operation1005 involves a few particular steps to monitor the optical transitionon the slowest optically switchable device 1091. These steps arepresented within the dotted box labeled 1005. Specifically, after theslowest optically switchable device 1091 transitions for a period oftime (e.g., after applying V_(drive) for a duration), open circuitconditions are applied to the slowest optically switchable device 1091and the open circuit voltage, V_(oc), of the slowest opticallyswitchable device 1091 is measured in operation 1005 a. Operation 1005 ais analogous to operations 587 and 589 of FIG. 5E, for example. Inoperation 1005 b, the charge (or relatedly, the charge density)delivered to the slowest optically switchable device 1091 over thecourse of the optical transition is determined. Operation 1005 b isanalogous to operation 590 in FIG. 5E. In operation 1005 c, it isdetermined whether the V_(oc) and the charge (or charge density)delivered to the slowest optically switchable device over the course ofthe transition both indicate that the optical transition is nearlycomplete. Operation 1005 c is analogous to operation 591 in FIG. 5E. Thedetermination may be made by comparing the magnitude of the measuredV_(oc) to a target V_(oc) (sometimes this target is referred to asV_(target)), and by comparing the charge or charge density delivered toa target charge or target charge density. Where both the V_(oc) and thedelivered charge (or charge density) indicate that the opticaltransition on the largest optically switchable device 1091 is completeor nearly complete, the method continues with operation 1012, where thehold voltage is applied to the largest optically switchable device 1091.If either the V_(oc) or the charge/charge density indicate that thetransition is not yet nearing completion, the method continues withoperation 1005 d, where the applied voltage on the largest opticallyswitchable device 1091 is increased back to the drive voltage and thetransition on the largest optically switchable device 1091 continues foran additional duration. Operations 1005 a-1005 d may be repeated anumber of times, as needed.

While the largest/slowest optically switchable device 1091 istransitioning in operation 1005, the faster optically switchable devices1090 are transitioning, as well. Specifically, in operation 1006, thefaster optically switchable devices 1090 are transitioned toward theending optical state. However, before the faster optically switchabledevices 1090 reach the ending optical state, the transitions on thefaster optically switchable devices 1090 are paused for a duration inoperation 1008. As explained above, the pausing lengthens the switchingtime for the smaller/faster optically switchable devices 1090 such thatthey can match the switching time of the larger/slower opticallyswitchable device 1091.

Next, in operation 1010, the faster optically switchable devices 1090continue transitioning toward the ending optical state. In this example,operation 1010 involves particular steps to monitor the transitions onthe faster optically switchable devices 1090. These steps are presentedwithin the dotted box labeled 1010. In particular, operation 1010 ainvolves determining the charge (or charge density) delivered to each ofthe faster optically switchable devices 1090 during the transition. Inoperation 1010 b, it is determined whether the delivered charge (orcharge density) indicates that the optical transition on each of thefaster optically switchable devices 1090 is complete or nearly complete.This may involve comparing the charge (or charge density) delivered toeach of the faster optically switchable devices 1090 to a target chargeor target charge density. Advantageously, pausing the transitions asdescribed herein does not substantially affect the target charge orcharge density. As such, target charges and charge densities configuredor calibrated for particular transitions do not need to be modified toaccommodate the pauses. Similarly, the drive voltage (as well as otherswitching parameters such as ramp-to-drive rate and ramp-to-hold rate)does not need to be modified in order to accommodate the pauses. Each ofthe faster optically switchable devices 1090 may be consideredindividually in operation 1010 b. In cases where the delivered charge orcharge density indicates that the relevant optical transition is not yetcomplete or nearly complete, the method continues with operation 1010 c,where the drive voltage is continued to be applied to the fasteroptically switchable devices 1090. Operation 1010 c may be carried outon an individual basis. In other words, the drive voltage may continueto be applied to any optically switchable device that still requiresapplication of additional drive voltage. Operations 1008 and 1010 may berepeated any number of times. The duration of the pauses, as well as thenumber of pauses, can be tailored such that all of the opticallyswitchable devices in the group transition over approximately the sametotal time period and display approximately the same tint states overthe course of the transition.

When the delivered charge (or charge density) indicates that thetransition on a particular faster optically switchable device 1090 iscomplete or nearly complete, the hold voltage may be applied to therelevant faster optically switchable device 1090 in operation 1012. Thehold voltage may be applied to each optically switchable deviceindividually, without regard to whether the hold voltage is beingapplied to other optically switchable devices in the group. Typically,the duration and number of pauses used during the transitions of thefaster optically switchable devices 1090 can be chosen such that thehold voltage is applied to each optically switchable device atapproximately the same time, or over a short period of time. Thisensures that the switching time for all the windows in the group issubstantially the same, resulting in a visually appealing transition. Insome embodiments, the duration of one or more of the pauses (in somecases all of the pauses) may be at least about 30 seconds, at leastabout 1 minute, at least about 3 minutes, at least about 5 minutes, orat least about 10 minutes. Generally, shorter pauses can be used whenthe number of pauses increases (for a given group of opticallyswitchable devices).

FIG. 5M illustrates another method 1030 for transitioning a group ofoptically switchable devices, where the group includes at least onerelatively larger/slower device and at least one relativelysmaller/faster device. Like the methods described in FIGS. 5K and 5L,the method of FIG. 5M is described in the context of the group ofoptically switchable devices shown in FIG. 10. The method 1030 begins atoperation 1031, where a command is received to transition the group ofoptically switchable devices to an ending optical state. In thisexample, the ending optical state is referred to as Tint₄. At operation1033, it is determined which device in the group has the slowestswitching time (in FIG. 10 this will be device 1091). This device willdetermine the switching time for the group of optically switchabledevices. At operation 1034, the slowest optically switchable device 1091in the group is transitioned to the ending optical state (Tint₄). Whilethe slowest optically switchable device 1091 is transitioning toward theending optical state (Tint₄), the faster optically switchable devices1090 transition to a first intermediate optical state (Tint₂) inoperation 1035. Next, at operation 1037, the faster optically switchabledevices 1090 are maintained at the first intermediate optical state(Tint₂) for a duration. Next, the faster optically switchable devices1090 are transitioned to a second intermediate optical state (Tint₃) inoperation 1039, and this second intermediate optical state (Tint₃) ismaintained for a duration in operation 1041. Then, in operation 1043 thefaster optically switchable devices 1090 are transitioned to the endingoptical state (Tint₄). At operation 1045, a hold voltage is applied toeach optically switchable device as it reaches or nears the endingoptical state. Often, the durations over which the intermediate opticalstates are maintained can be selected to ensure that all of theoptically switchable devices reach the ending optical state atapproximately the same time (e.g., within about 1 minute, or withinabout 2 minutes, or within about 5 minutes, or within about 10 minutes,or within about 15 minutes in various cases). The exact timing of wheneach optically switchable device reaches the ending optical state may beless important than ensuring that the optical states of the differentoptically switchable devices in the group are approximately matching oneanother throughout the transition. In some embodiments, all theoptically switchable devices in the group may display approximately thesame optical state/tint level throughout the transition. In someimplementations, the optical density of the slowest optically switchabledevice may be within about 0.1, 0.2, 0.3, 0.4, or 0.5 of the opticaldensity of the faster optically switchable devices in the group, at allpoints in time during the transition. In other words, the difference inoptical density between the slowest optically switchable device and thefaster optically switchable devices in the group may be about 0.5 orless, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less, at allpoints in time during the transition. In some embodiments, the maximumdifference in optical density between the slowest optically switchabledevice and the faster optically switchable devices in the group, overthe course of the entire transition, may be between about 0.1-0.5, orbetween about 0.1-0.4, or between about 0.2-0.3. The optical densitymentioned here refers to the optical density at the center of eachoptically switchable device at a given point in time.

While the method 1030 of FIG. 5M describes three active transitioningperiods (operations 1035, 1039, and 1043) resulting in two intermediateoptical states for the faster optically switchable devices 1090, anynumber of transitioning periods and intermediate optical states can beused. While operations 1037 and 1041 are described in terms ofmaintaining the faster optically switchable devices at particularintermediate optical states, it is understood that the optical state ofthe faster optically switchable devices may be slowly changing over thecourse of these operations. Further details are provided below.

Any of the methods described herein can be used to monitor any of thetransitions described in FIG. 5M (e.g., during operations 1034, 1035,1039, and 1043). In one embodiment, the method of FIG. 5E may be used tomonitor one or more of these transitions. Generally speaking, the method1030 of FIG. 5M is similar to the methods 1000 and 1020 of FIGS. 5K and5L. The pausing periods described in relation to FIGS. 5K and 5L aresimilar to the periods during which an intermediate optical state ismaintained in FIG. 5M.

One difference between these methods may be the way in which the opticaltransitions are defined and monitored. For instance, in some embodimentsof FIG. 5K or 5L, the determination of when to apply the hold voltage toeach of the faster optically switchable devices may be made based ondata related to the full optical transition from the starting opticalstate (e.g., at operation 1002) to the ending optical state. Bycontrast, in some embodiments of FIG. 5M, the determination of when toapply the hold voltage to each of the faster optically switchabledevices may be made based on data related to the optical transition fromthe last intermediate optical state (e.g., Tint₃ in FIG. 5M) to theending optical state (e.g., Tint₄ in FIG. 5M).

Relatedly, in some embodiments of FIG. 5M, each individual transition(e.g., from the starting optical state→Tint₂, Tint₂→Tint₃, andTint₃→Tint₄) on the faster optically switchable devices can be monitoredbased on data related to the particular starting and ending opticalstates for each individual transition. In the methods of FIGS. 5K and5L, there may not be any need to actively monitor all of the individualportions of the transition. In various embodiments of FIGS. 5K and 5L,the transition may be monitored only during the final transitioningperiod (e.g., the transitioning period after the final pause). Theending points of the earlier (non-final) portions of the transition maybe determined based solely on timing (which may be selected based on thefactors described above), without regard to feedback.

In various embodiments, the optically switchable devices may be providedtogether on a network. In some cases, a communication network may beused to control the various optically switchable devices. In oneexample, a master controller may communicate with one or more networkcontrollers, which may each communicate with one or more windowcontrollers. Each window controller may control one or more individualoptically switchable devices. An example communication network,including the different types of controllers, is described in U.S.Provisional Patent Application No. 62/248,181, filed Oct. 29, 2015, andtitled “CONTROLLERS FOR OPTICALLY-SWITCHABLE DEVICES,” which is hereinincorporated by reference in its entirety. The methods described hereinmay be implemented on a window controller, a network controller, and/ora master controller, as desired for a particular application. In someembodiments, a master controller and/or network controller may be usedto assess the parameters/switching characteristics of all the opticallyswitchable devices in the group or zone, in order to determine, e.g.,which optically switchable device transitions slowest, and targetswitching time for the group. The master controller and/or networkcontroller may determine the switching parameters that should be used(e.g., ramp-to-drive rate, drive voltage, ramp-to-hold rate, holdvoltage, number of pauses, duration of pauses, intermediate opticalstates, etc.) for each optically switchable device in the group. Themaster controller and/or network controller may then provide theseswitching parameters (or some subset thereof) to the window controllers,which may then implement the transition on each optically switchabledevice as appropriate.

While the methods described in FIGS. 5K-5M are presented in the contextof FIG. 10 where one large optically switchable device 1091 issurrounded by a number of smaller optically switchable devices 1090 ofequal size, the methods are not so limited. Generally, the methodsdescribed in FIGS. 5K-5M are useful any time there is a group ofoptically switchable devices that transition at two or more differentrates/transition times, where it is desired that every opticallyswitchable device in the group transitions over substantially the sametime period.

In many cases, the group of optically switchable devices will include atleast one optically switchable device that is relatively smaller andtransitions faster, and at least one optically switchable device that isrelatively larger and transitions slower. The total switching time ischosen to approximate the switching time for the slowest opticallyswitchable device in the group. The group may include opticallyswitchable devices having a number of different sizes/switching times.The number and duration of the pauses for each window can be selectedindependently as described herein to ensure that all of the opticallyswitchable devices reach the ending optical state at approximately thesame time. For instance, in one embodiment the group of opticallyswitchable devices includes two 60″ devices, two 30″ devices, four 14″devices, and one 12″ device. In this example, the largest/slowestoptically switchable devices (which will determine the total switchingtime for the group) are the two 60″ devices, which may transitionwithout any pauses. The two 30″ devices may each transition using asingle pause (n=1), the four 14″ devices may each transition using twopauses (n=2), and the 12″ device may transition using three pauses(n=3). The number and duration of pauses may be the same or differentfor various optically switchable devices in the group.

The different optically switchable devices in the group may or may notstart at the same starting optical states, and may or may not end at thesame ending optical states. While the methods are particularly useful incases where it is desired to approximately match the tint states overthe different devices over the course of a transition, the methods mayalso be used in cases where the absolute tint state of each device isunimportant. In some such cases, it may be desirable to match tintingtimes across different devices, even if it is not important to match thetinting states across the different devices.

In some embodiments, it is desirable to stagger the activetransitions/pauses among the different optically switchable devices suchthat the peak power provided to the group of optically switchabledevices is minimized. This minimization of peak power maximizes thenumber of optically switchable devices that can be provided along aparticular portion of a power distribution network used to route powerto the optically switchable devices, and may avoid the need to usehigher rated (e.g., class 1, as opposed to class 2) hardware (e.g.,power supplies, cabling, etc.) that may be more costly.

For example, if all of the faster optically switchable devices activelytransition and pause their optical transitions at the same time, thepower drawn by the group of devices will substantially decrease duringthe pause. When the pause is over, the power drawn by the group ofdevices will substantially increase (since all of the devices are beingdriven simultaneously). Conversely, if the active transitions and pausesare staggered in time such that some of the faster optically switchabledevices continue to actively transition while others pause, thissubstantial increase in power can be avoided, and the power delivered tothe group of optically switchable devices can be more uniform over time.The staggering may be accomplished by dividing the faster opticallyswitchable devices into sub-groups. Within the sub-groups, the opticallyswitchable devices may actively transition/pause together. Betweendifferent sub-groups, the optically switchable devices may activelytransition/pause at different times. The sub-groups may be as small asan individual optically switchable device.

In the context of FIG. 10, for example, the faster optically switchabledevices 1090 may be broken into three sub-groups (e.g., the left group,the top group, and the right group). The devices in the left group maypause first, the devices in the top group may pause second, and thedevices in the right group may pause third. The staggered pauses andactive transitions can be cycled as desired. The pauses (and/or activetransitions) may or may not overlap, depending on the transitions anddevices involved, as well as the selected number/duration of the pauses.

In some embodiments, different modes may be used for different types oftransitions, with different switching behavior for each mode. In oneexample, a first mode may be used in the case of a normal opticaltransition. The optical transition may be from a known starting opticalstate to a known ending optical state. A second mode may be used in thecase where an interrupt command is received to transition the devices toa different ending optical state. In other words, this mode may be usedin the case where an ongoing optical transition on a given device isinterrupted by a command to transition the device to a different endingoptical state. In the first mode, the optically switchable devices maytransition according to the method 1000 of FIG. 5K. In the second mode,after an interrupt command is received, the optically switchable devicesmay transition using a different method, for example one that does notinvolve pausing any of the transitions. In the second mode, all of theoptically switchable devices may transition as quickly as possible tothe new ending optical state.

Other methods for ensuring a uniform transition time for a group ofoptically switchable devices that includes at least one relativelysmall/quick device and at least one relatively large/slow device may beused in some cases. For instance, the transitions on the fasteroptically switchable devices can be slowed by using a lowerramp-to-drive rate and/or by using a lower drive voltage. Theramp-to-drive rate and the drive voltage are discussed further inrelation to FIGS. 2 and 3. In many cases, smaller/faster devices arealready driven using smaller ramp-to-drive rates and/or smaller drivevoltages compared to larger/slower devices, at least partially becausethe larger/slower devices are capable of withstanding greater appliedvoltages without damage. Further decreasing the ramp-to-drive rateand/or the drive voltage can slow the transition of the faster opticallyswitchable devices. However, certain problems can arise with theseapproaches. For instance, these methods may result in slow-to-starttransitions on the faster optically switchable devices. By comparison,the transitions on the larger/slower optically switchable devices arevisually perceptible earlier. The result is that toward the beginning ofthe transition, it appears that the large/slow device is starting totransition, while the smaller/faster devices do not appear to bereacting. While the various devices may reach the ending optical stateat approximately the same time, the differences in visual appearancebetween the different devices near the beginning of the transition isundesirable.

Another possible issue with the low ramp-to-drive and low drive voltagemethods is that at these conditions it can become difficult to monitorthe optical transitions on the smaller/faster devices. This isespecially significant in cases where monitoring the transition involvesdetermining an amount of charge or charge density delivered to a device.The difficulty may arise because the current supplied to the devices inthese embodiments is fairly low (as a result of the low ramp-to-driverate and/or low drive voltage), and the error associated with measuringsuch current may be relatively high (e.g., depending on the controllerthat is used). Because the error may be large in comparison to themeasured value, it becomes difficult or impossible to monitor thetransition on the fast optically switchable device. Therefore, there isa limit to how low the ramp-to-drive rate and drive voltage can be,while still maintaining good control over the various opticaltransitions. The methods described in FIGS. 5K-5M overcome this issue bypausing the transitions on the faster optically switchable devices(FIGS. 5K and 5L) or by breaking up the transition on the fasteroptically switchable devices into a number of smaller individualtransitions separated by pauses (FIG. 5M).

A number of different options are available in terms of what ishappening to the faster optically switchable devices while thetransitions on such devices are paused (as described in relation toFIGS. 5K and 5L) and/or while such devices are maintaining anintermediate optical state (as described in relation to FIG. 5M). Forthe sake of brevity, both of these techniques will be referred to as apause. In one example, open circuit conditions are applied during thepause. In this embodiment, the current passed to the device will fall tozero during the pause. The optical state of the device may remainsubstantially unchanged during the duration of the pause (except for anycenter-to-edge differences in tint state for the device, which may beminimized over the course of the pause). In some cases, the opticalstate of the device may relax back toward the starting optical stateduring the pause.

In another example, an applied voltage may be provided to the deviceduring the pause. In one embodiment, open circuit conditions are appliedto the device and V_(oc) is measured shortly before the pause. Theapplied voltage during the pause may correspond to the most recentlymeasured V_(oc) on the device. In this embodiment, the current deliveredto the device falls substantially during the pause, but does not stopcompletely. The device will continue to transition at a lower rateduring the pause. In another embodiment, the applied voltage during thepause may be pre-determined. Different pauses may have differentpre-determined applied voltages. For instance, in one example, a fasteroptically switchable device transitions over three periods of activetransitioning separated by two periods of pausing. During the firstpause, the applied voltage may be about −0.5V, and during the secondpause, the applied voltage may be about −1.0V. The applied voltages maybe determined based on the voltage applied before the transition, thehold voltage applied at the end of the transition, and the number ofpauses. For example, if a single pause is used, the applied voltageduring the pause may be selected to be about halfway between the voltageapplied before the transition and the hold voltage applied at the end ofthe transition. In another example where two pauses are used, theapplied voltage during the first pause may be selected to be about ⅓ ofthe way between the voltage applied before the transition and the holdvoltage applied at the end of the transition, and the applied voltageduring the second pause may be selected to be about ⅔ of the way betweenthe voltage applied before the transition and the hold voltage appliedat the end of the transition. This example can be generalized to includeany number of pauses. Other methods for specifying the applied voltageduring each pause can also be used. In embodiments where apre-determined voltage is applied during a pause, the current deliveredto the device may fall substantially during the pause, but may not stopentirely. The device may continue to transition at a lower rate duringthe pause.

FIGS. 11A and 11B present experimental results related to the methoddescribed in FIG. 5K. Each graph illustrates the optical density at thecenter of certain optically switchable devices vs. time over the courseof one or more optical transitions on the optically switchable devices.FIG. 11A relates to an optical transition from a relatively clear state(Tint₁) to a relatively dark state (Tint₄), and FIG. 11B relates to anoptical transition from a relatively dark state (Tint₄) to a relativelyclear state (Tint₁). FIGS. 11A and 11B each illustrate one opticaltransition on a 58″ optically switchable device (without pausing) andtwo different optical transitions on a 14″ optically switchable device,one of which involves pausing and the other of which does not. Withreference to FIG. 11A, line 1102 relates to the transition on the 14″device where no pausing is used, line 1104 relates to the transition onthe 14″ device where two pauses are used, and line 1106 relates to thetransition on the 58″ device. With reference to FIG. 11B, line 1112relates to the transition on the 14″ device where no pausing is used,line 1114 relates to the transition on the 14″ device where two pausesare used, and line 1116 relates to the transition on the 58″ device. Thepauses are correlated with periods where the optical density on the 14″device changes much less substantially compared to the non-paused (e.g.,active transitioning) periods.

From FIGS. 11A and 11B, it can be seen that if no pauses are used, the14″ device will reach the ending optical state much quicker than the 58″device. Visually, this means that the 14″ device tints (or untints)out-of-sync with the 58″ device, and there is a significant mis-matchbetween the optical states on the differently sized devices at any giventime. By contrast, when the 14″ device transitions using pauses, thedevices' transition times are much more similar. The visual result isthat there is substantially less mis-match between the optical states ofthe differently sized devices at any given time.

FIG. 11C is a graph illustrating optical density vs. time over thecourse of two optical transitions (Tint₁→Tint₄, and then Tint₄→Tint₁)for a 24″ optically switchable device where either no pausing is used(line 1120), a single pause at open circuit conditions is used (line1122), or where a single pause at a particular voltage is used (line1124). This figure illustrates what is happening to the optical state ofthe devices during different kinds of pauses. Where the transitions arepaused at open circuit conditions (line 1122), the optical densityquickly evens out and remains substantially the same during the pause.Where the transitions are paused at a particular applied voltage (e.g.,the last measured open circuit voltage, or a pre-set voltage), theoptical density continues to change, but at a lower rate.

In some embodiments, the rate of change of the open circuit voltage(dV_(oc)/dt) may be monitored in addition to the open circuit voltageitself. An additional step may be provided where the magnitude ofdV_(oc)/dt is compared against a maximum value to ensure that the drivevoltage is modified in a manner that ensures V_(oc) is not changing tooquickly. This additional step may be used in any of the methods hereinthat utilize V_(oc) measurements.

In certain implementations, the method involves using a static offset tothe hold voltage. This offset hold voltage may be used to probe thedevice and elicit a current response, as described in relation to FIGS.5A, 5B, and 5D. The offset hold voltage may also be used as a targetopen circuit voltage, as described in relation to FIGS. 5C, and 5E, 5G,and 5J. In certain cases, particularly for windows with a largeseparation between the bus bars (e.g., at least about 25″), the offsetcan be beneficial in ensuring that the optical transition proceeds tocompletion across the entire window.

In many cases, an appropriate offset is between about 0-0.5V (e.g.,about 0.1-0.4V, or between about 0.1-0.2V). Typically, the magnitude ofan appropriate offset increases with the size of the window. An offsetof about 0.2V may be appropriate for a window of about 14 inches, and anoffset of about 0.4V may be appropriate for a window of about 60 inches.These values are merely examples and are not intended to be limiting. Insome embodiments, a window controller is programmed to use a staticoffset to V_(hold). The magnitude and in some cases direction of thestatic offset may be based on the device characteristics such as thesize of the device and the distance between the bus bars, the drivingvoltage used for a particular transition, the leakage current of thedevice, the peak current density, capacitance of the device, etc. Invarious embodiments, the static offset is determined empirically. Insome designs, it is calculated dynamically, when the device is installedor while it is installed and operating, from monitored electrical and/oroptical parameters or other feedback.

In other embodiments, a window controller may be programmed todynamically calculate the offset to V_(hold). In one implementation, thewindow controller dynamically calculates the offset to V_(hold) based onone or more of the device's current optical state (OD), the currentdelivered to the device (I), the rate of change of current delivered tothe device (dI/dt), the open circuit voltage of the device (V_(oc)), andthe rate of change of the open circuit voltage of the device(dV_(oc)/dt). This embodiment is particularly useful because it does notrequire any additional sensors for controlling the transition. Instead,all of the feedback is generated by pulsing the electronic conditionsand measuring the electronic response of the device. The feedback, alongwith the device characteristics mentioned above, may be used tocalculate the optimal offset for the particular transition occurring atthat time. In other embodiments, the window controller may dynamicallycalculate the offset to V_(hold) based on certain additional parameters.These additional parameters may include the temperature of the device,ambient temperature, and signals gathered by photoptic sensors on thewindow. These additional parameters may be helpful in achieving uniformoptical transitions at different conditions. However, use of theseadditional parameters also increases the cost of manufacture due to theadditional sensors required.

The offset may be beneficial in various cases due to the non-uniformquality of the effective voltage, V_(eff), applied across the device.The non-uniform V_(eff) is shown in FIG. 2, for example, describedabove. Because of this non-uniformity, the optical transition does notoccur in a uniform manner. In particular, areas near the bus barsexperience the greatest V_(eff) and transition quickly, while areasremoved from the bus bars (e.g., the center of the window) experiencethe lowest V_(eff) and transition more slowly. The offset can helpensure that the optical transition proceeds to completion at the centerof the device where the change is slowest.

FIGS. 6A and 6B show graphs depicting the total charge delivered overtime and the applied voltage over time during two differentelectrochromic tinting transitions. The window in each case measuredabout 24×24 inches. The total charge delivered is referred to as theTint Charge Count, and is measured in coulombs (C). The total chargedelivered is presented on the left hand y-axis of each graph, and theapplied voltage is presented on the right hand y-axis of each graph. Ineach figure, line 602 corresponds to the total charge delivered and line604 corresponds to the applied voltage. Further, line 606 in each graphcorresponds to a threshold charge (the threshold charge densitymultiplied by the area of the window), and line 608 corresponds to atarget open circuit voltage. The threshold charge and target opencircuit voltage are used in the method shown in FIG. 5E tomonitor/control the optical transition.

The voltage curves 604 in FIGS. 6A and 6B each start out with a ramp todrive component, where the magnitude of the voltage ramps up to thedrive voltage of about −2.5V. After an initial period of applying thedrive voltage, the voltage begins to spike upwards at regular intervals.These voltage spikes occur when the electrochromic device is beingprobed. As described in FIG. 5E, the probing occurs by applying opencircuit conditions to the device. The open circuit conditions result inan open circuit voltage, which correspond to the voltage spikes seen inthe graphs. Between each probe/open circuit voltage, there is anadditional period where the applied voltage is the drive voltage. Inother words, the electrochromic device is driving the transition andperiodically probing the device to test the open circuit voltage andthereby monitor the transition. The target open circuit voltage,represented by line 608, was selected to be about −1.4V for each case.The hold voltage in each case was about −1.2V. Thus, the target opencircuit voltage was offset from the hold voltage by about 0.2V.

In the transition of FIG. 6A, the magnitude of the open circuit voltageexceeds the magnitude of the target open circuit voltage at about 1500seconds. Because the relevant voltages in this example are negative,this is shown in the graph as the point at which the open circuitvoltage spikes first fall below the target open circuit voltage. In thetransition of FIG. 6B, the magnitude of the open circuit voltage exceedsthe magnitude of the target open circuit voltage sooner than in FIG. 6A,around 1250 seconds.

The total delivered charge count curves 602 in FIGS. 6A and 6B eachstart at 0 and rise monotonically. In the transition of FIG. 6A, thedelivered charge reaches the threshold charge at around 1500 seconds,which was very close to the time at which the target open circuitvoltage was met. Once both conditions were met, the voltage switchedfrom the drive voltage to the hold voltage, around 1500 seconds. In thetransition of FIG. 6B, the total delivered charge took about 2100seconds to reach the charge threshold, which is about 14 minutes longerthan it took the voltage to reach the target voltage for thistransition. After both the target voltage and threshold charge are met,the voltage is switched to the hold voltage. The additional requirementof the total charge delivered results in the FIG. 6B case driving thetransition at the drive voltage for a longer time than might otherwisebe used. This helps ensure full and uniform transitions across manywindow designs at various environmental conditions.

In another embodiment, the optical transition is monitored throughvoltage sensing pads positioned directly on the transparent conductivelayers (TCLs). This allows for a direct measurement of the V_(eff) atthe center of the device, between the bus bars where V_(eff) is at aminimum. In this case, the controller indicates that the opticaltransition is complete when the measured V_(eff) at the center of thedevice reaches a target voltage such as the hold voltage. In variousembodiments, the use of sensors may reduce or eliminate the benefit fromusing a target voltage that is offset from the hold voltage. In otherwords, the offset may not be needed and the target voltage may equal thehold voltage when the sensors are present. Where voltage sensors areused, there should be at least one sensor on each TCL. The voltagesensors may be placed at a distance mid-way between the bus bars,typically off to a side of the device (near an edge) so that they do notaffect (or minimally affect) the viewing area. The voltage sensors maybe hidden from view in some cases by placing them proximate aspacer/separator and/or frame that obscures the view of the sensor.

FIG. 6C presents an embodiment of an EC window 690 that utilizes sensorsto directly measure the effective voltage at the center of the device.The EC window 690 includes top bus bar 691 and bottom bus bar 692, whichare connected by wires 693 to a controller (not shown). Voltage sensor696 is placed on the top TCL, and voltage sensor 697 is placed on thebottom TCL. The sensors 696 and 697 are placed at a distance mid-waybetween the bus bars 691 and 692, though they are off to the side of thedevice. In some cases the voltage sensors may be positioned such thatthey reside within a frame of the window. This placement helps hide thesensors and promote optimal viewing conditions. The voltage sensors 696and 697 are connected to the controller through wires 698. The wires 693and 698 may pass under or through a spacer/separator placed and sealedin between the panes of the window. The window 690 shown in FIG. 6C mayutilize any of the methods described herein for controlling an opticaltransition.

In some implementations, the voltage sensing pads may be conductive tapepads. The pads may be as small as about 1 mm² in some embodiments. Inthese or other cases, the pads may be about 10 mm² or less. A four wiresystem may be used in embodiments utilizing such voltage sensing pads.

Electrochromic Devices and Controllers—Examples

Examples of electrochromic device structure and fabrication will now bepresented. FIGS. 7A and 7B are schematic cross-sections of anelectrochromic device, 700, showing a common structural motif for suchdevices. Electrochromic device 700 includes a substrate 702, aconductive layer (CL) 704, an electrochromic layer (EC) 706, an optionalion conducting (electronically resistive) layer (IC) 708, a counterelectrode layer (CE) 710, and another conductive layer (CL) 712.Elements 704, 706, 708, 710, and 712 are collectively referred to as anelectrochromic stack, 714. In numerous embodiments, the stack does notcontain ion conducting layer 708, or at least not as a discrete orseparately fabricated layer. A voltage source, 716, operable to apply anelectric potential across electrochromic stack 712 effects thetransition of the electrochromic device from, e.g., a clear state (referto FIG. 7A) to a tinted state (refer to FIG. 7B).

The order of layers may be reversed with respect to the substrate. Thatis, the layers may be in the following order: substrate, conductivelayer, counter electrode layer, ion conducting layer, electrochromicmaterial layer, and conductive layer. The counter electrode layer mayinclude a material that is electrochromic or not. If both theelectrochromic layer and the counter electrode layer employelectrochromic materials, one of them should be a cathodically coloringmaterial and the other should be an anodically coloring material. Forexample, the electrochromic layer may employ a cathodically coloringmaterial and the counter electrode layer may employ an anodicallycoloring material. This is the case when the electrochromic layer is atungsten oxide and the counter electrode layer is a nickel tungstenoxide.

The conductive layers commonly comprise transparent conductivematerials, such as metal oxides, alloy oxides, and doped versionsthereof, and are commonly referred to as “TCO” layers because they aremade from transparent conducting oxides. In general, however, thetransparent layers can be made of any transparent, electronicallyconductive material that is compatible with the device stack. Some glasssubstrates are provided with a thin transparent conductive oxide layersuch as fluorinated tin oxide, sometimes referred to as “FTO.”

Device 700 is meant for illustrative purposes, in order to understandthe context of embodiments described herein. Methods and apparatusdescribed herein are used to identify and reduce defects inelectrochromic devices, regardless of the structural arrangement of theelectrochromic device.

During normal operation, an electrochromic device such as device 700reversibly cycles between a clear state and a tinted state. As depictedin FIG. 7A, in the clear state, a potential is applied across theelectrodes (transparent conductor layers 704 and 712) of electrochromicstack 714 to cause available ions (e.g. lithium ions) in the stack toreside primarily in the counter electrode 710. If electrochromic layer706 contains a cathodically coloring material, the device is in a clearstate. In certain electrochromic devices, when loaded with the availableions, counter electrode layer 710 can be thought of as an ion storagelayer.

Referring to FIG. 7B, when the potential on the electrochromic stack isreversed, the ions are transported across ion conducting layer 708 toelectrochromic layer 706 and cause the material to enter the tintedstate. Again, this assumes that the optically reversible material in theelectrochromic device is a cathodically coloring electrochromicmaterial. In certain embodiments, the depletion of ions from the counterelectrode material causes it to color also as depicted. In other words,the counter electrode material is anodically coloring electrochromicmaterial. Thus, layers 706 and 710 combine to reduce the amount of lighttransmitted through the stack. When a reverse voltage is applied todevice 700, ions travel from electrochromic layer 706, through the ionconducting layer 708, and back into counter electrode layer 710. As aresult, the device clears.

Some pertinent examples of electrochromic devices are presented in thefollowing US patent applications, each incorporated by reference in itsentirety: U.S. patent application Ser. No. 12/645,111, filed Dec. 22,2009; U.S. patent application Ser. No. 12/772,055, filed Apr. 30, 2010;U.S. patent application Ser. No. 12/645,159, filed Dec. 22, 2009; U.S.patent application Ser. No. 12/814,279, filed Jun. 11, 2010; U.S. patentapplication Ser. No. 13/462,725, filed May 2, 2012 and U.S. patentapplication Ser. No. 13/763,505, filed Feb. 8, 2013.

Electrochromic devices such as those described in relation to FIGS. 7Aand 7B are used in, for example, electrochromic windows. For example,substrate 702 may be architectural glass upon which electrochromicdevices are fabricated. Architectural glass is glass that is used as abuilding material. Architectural glass is typically used in commercialbuildings, but may also be used in residential buildings, and typically,though not necessarily, separates an indoor environment from an outdoorenvironment. In certain embodiments, architectural glass is at least 20inches by 20 inches, and can be much larger, e.g., as large as about 72inches by 120 inches.

In some embodiments, electrochromic glass is integrated into aninsulating glass unit (IGU). An insulating glass unit includes multipleglass panes assembled into a unit, generally with the intention ofmaximizing the thermal insulating properties of a gas contained in thespace formed by the unit while at the same time providing clear visionthrough the unit. Insulating glass units incorporating electrochromicglass are similar to insulating glass units currently known in the art,except for electrical terminals for connecting the electrochromic glassto voltage source.

The optical transition driving logic can be implemented in manydifferent controller configurations and coupled with other controllogic. Various examples of suitable controller design and operation areprovided in the following patent applications, each incorporated hereinby reference in its entirety: U.S. patent application Ser. No.13/049,623, filed Mar. 16, 2011; U.S. patent application Ser. No.13/049,756, filed Mar. 16, 2011; U.S. Pat. No. 8,213,074, filed Mar. 16,2011; U.S. patent application Ser. No. 13/449,235, filed Apr. 17, 2012;U.S. patent application Ser. No. 13/449,248, filed Apr. 17, 2012; U.S.patent application Ser. No. 13/449,251, filed Apr. 17, 2012; U.S. patentapplication Ser. No. 13/326,168, filed Dec. 14, 2011; U.S. patentapplication Ser. No. 13/682,618, filed Nov. 20, 2012; and U.S. patentapplication Ser. No. 13/772,969, filed Feb. 21, 2013. The followingdescription and associated figures, FIGS. 8 and 9, present certainnon-limiting controller design options suitable for implementing thedrive profiles described herein.

FIG. 8 shows a cross-sectional axonometric view of an embodiment of anIGU 102 that includes two window panes or lites 216 and a controller250. In various embodiments, IGU 102 can include one, two, or moresubstantially transparent (e.g., at no applied voltage) lites 216 aswell as a frame, 218, that supports the lites 216. For example, the IGU102 shown in FIG. 9 is configured as a double-pane window. One or moreof the lites 216 can itself be a laminate structure of two, three, ormore layers or lites (e.g., shatter-resistant glass similar toautomotive windshield glass). In IGU 102, at least one of the lites 216includes an electrochromic device or stack, 220, disposed on at leastone of its inner surface, 222, or outer surface, 224: for example, theinner surface 222 of the outer lite 216.

In multi-pane configurations, each adjacent set of lites 216 can have aninterior volume, 226, disposed between them. Generally, each of thelites 216 and the IGU 102 as a whole are rectangular and form arectangular solid. However, in other embodiments other shapes (e.g.,circular, elliptical, triangular, curvilinear, convex, concave) may bedesired. In some embodiments, the volume 226 between the lites 116 isevacuated of air. In some embodiments, the IGU 102 ishermetically-sealed. Additionally, the volume 226 can be filled (to anappropriate pressure) with one or more gases, such as argon (Ar),krypton (Kr), or xenon (Xn), for example. Filling the volume 226 with agas such as Ar, Kr, or Xn can reduce conductive heat transfer throughthe IGU 102 because of the low thermal conductivity of these gases. Thelatter two gases also can impart improved acoustic insulation due totheir increased weight.

In some embodiments, frame 218 is constructed of one or more pieces. Forexample, frame 218 can be constructed of one or more materials such asvinyl, PVC, aluminum (Al), steel, or fiberglass. The frame 218 may alsoinclude or hold one or more foam or other material pieces that work inconjunction with frame 218 to separate the lites 216 and to hermeticallyseal the volume 226 between the lites 216. For example, in a typical IGUimplementation, a spacer lies between adjacent lites 216 and forms ahermetic seal with the panes in conjunction with an adhesive sealantthat can be deposited between them. This is termed the primary seal,around which can be fabricated a secondary seal, typically of anadditional adhesive sealant. In some such embodiments, frame 218 can bea separate structure that supports the IGU construct.

Each lite 216 includes a substantially transparent or translucentsubstrate, 228. Generally, substrate 228 has a first (e.g., inner)surface 222 and a second (e.g., outer) surface 224 opposite the firstsurface 222. In some embodiments, substrate 228 can be a glasssubstrate. For example, substrate 228 can be a conventional siliconoxide (SO_(x))-based glass substrate such as soda-lime glass or floatglass, composed of, for example, approximately 75% silica (SiO₂) plusNa₂O, CaO, and several minor additives. However, any material havingsuitable optical, electrical, thermal, and mechanical properties may beused as substrate 228. Such substrates also can include, for example,other glass materials, plastics and thermoplastics (e.g., poly(methylmethacrylate), polystyrene, polycarbonate, allyl diglycol carbonate, SAN(styrene acrylonitrile copolymer), poly(4-methyl-1-pentene), polyester,polyamide), or mirror materials. If the substrate is formed from, forexample, glass, then substrate 228 can be strengthened, e.g., bytempering, heating, or chemically strengthening. In otherimplementations, the substrate 228 is not further strengthened, e.g.,the substrate is untempered.

In some embodiments, substrate 228 is a glass pane sized for residentialor commercial window applications. The size of such a glass pane canvary widely depending on the specific needs of the residence orcommercial enterprise. In some embodiments, substrate 228 can be formedof architectural glass. Architectural glass is typically used incommercial buildings, but also can be used in residential buildings, andtypically, though not necessarily, separates an indoor environment froman outdoor environment. In certain embodiments, a suitable architecturalglass substrate can be at least approximately 20 inches by approximately20 inches, and can be much larger, for example, approximately 80 inchesby approximately 120 inches, or larger. Architectural glass is typicallyat least about 2 millimeters (mm) thick and may be as thick as 6 mm ormore. Of course, electrochromic devices 220 can be scalable tosubstrates 228 smaller or larger than architectural glass, including inany or all of the respective length, width, or thickness dimensions. Insome embodiments, substrate 228 has a thickness in the range ofapproximately 1 mm to approximately 10 mm. In some embodiments,substrate 228 may be very thin and flexible, such as Gorilla Glass® orWillow™ Glass, each commercially available from Corning, Inc. ofCorning, N.Y., these glasses may be less than 1 mm thick, as thin as 0.3mm thick.

Electrochromic device 220 is disposed over, for example, the innersurface 222 of substrate 228 of the outer pane 216 (the pane adjacentthe outside environment). In some other embodiments, such as in coolerclimates or applications in which the IGUs 102 receive greater amountsof direct sunlight (e.g., perpendicular to the surface of electrochromicdevice 220), it may be advantageous for electrochromic device 220 to bedisposed over, for example, the inner surface (the surface bordering thevolume 226) of the inner pane adjacent the interior environment. In someembodiments, electrochromic device 220 includes a first conductive layer(CL) 230 (often transparent), an electrochromic layer (EC) 232, an ionconducting layer (IC) 234, a counter electrode layer (CE) 236, and asecond conductive layer (CL) 238 (often transparent). Again, layers 230,232, 234, 236, and 238 are also collectively referred to aselectrochromic stack 220.

A power source 240 operable to apply an electric potential (V_(app)) tothe device and produce V_(eff) across a thickness of electrochromicstack 220 and drive the transition of the electrochromic device 220from, for example, a clear or lighter state (e.g., a transparent,semitransparent, or translucent state) to a tinted or darker state(e.g., a tinted, less transparent or less translucent state). In someother embodiments, the order of layers 230, 232, 234, 236, and 238 canbe reversed or otherwise reordered or rearranged with respect tosubstrate 238.

In some embodiments, one or both of first conductive layer 230 andsecond conductive layer 238 is formed from an inorganic and solidmaterial. For example, first conductive layer 230, as well as secondconductive layer 238, can be made from a number of different materials,including conductive oxides, thin metallic coatings, conductive metalnitrides, and composite conductors, among other suitable materials. Insome embodiments, conductive layers 230 and 238 are substantiallytransparent at least in the range of wavelengths where electrochromismis exhibited by the electrochromic layer 232. Transparent conductiveoxides include metal oxides and metal oxides doped with one or moremetals. For example, metal oxides and doped metal oxides suitable foruse as first or second conductive layers 230 and 238 can include indiumoxide, indium tin oxide (ITO), doped indium oxide, tin oxide, doped tinoxide, zinc oxide, aluminum zinc oxide, doped zinc oxide, rutheniumoxide, doped ruthenium oxide, among others. As indicated above, firstand second conductive layers 230 and 238 are sometimes referred to as“transparent conductive oxide” (TCO) layers.

In some embodiments, commercially available substrates, such as glasssubstrates, already contain a transparent conductive layer coating whenpurchased. In some embodiments, such a product can be used for bothsubstrate 238 and conductive layer 230 collectively. Examples of suchglass substrates include conductive layer-coated glasses sold under thetrademark TEC Glass™ by Pilkington, of Toledo, Ohio and SUNGATE™ 300 andSUNGATE™ 500 by PPG Industries of Pittsburgh, Pa. Specifically, TECGlass™ is, for example, a glass coated with a fluorinated tin oxideconductive layer.

In some embodiments, first or second conductive layers 230 and 238 caneach be deposited by physical vapor deposition processes including, forexample, sputtering. In some embodiments, first and second conductivelayers 230 and 238 can each have a thickness in the range ofapproximately 0.01 μm to approximately 1 μm. In some embodiments, it maybe generally desirable for the thicknesses of the first and secondconductive layers 230 and 238 as well as the thicknesses of any or allof the other layers described below to be individually uniform withrespect to the given layer; that is, that the thickness of a given layeris uniform and the surfaces of the layer are smooth and substantiallyfree of defects or other ion traps.

A primary function of the first and second conductive layers 230 and 238is to spread an electric potential provided by a power source 240, suchas a voltage or current source, over surfaces of the electrochromicstack 220 from outer surface regions of the stack to inner surfaceregions of the stack. As mentioned, the voltage applied to theelectrochromic device experiences some Ohmic potential drop from theouter regions to the inner regions as a result of a sheet resistance ofthe first and second conductive layers 230 and 238. In the depictedembodiment, bus bars 242 and 244 are provided with bus bar 242 incontact with conductive layer 230 and bus bar 244 in contact withconductive layer 238 to provide electric connection between the voltageor current source 240 and the conductive layers 230 and 238. Forexample, bus bar 242 can be electrically coupled with a first (e.g.,positive) terminal 246 of power source 240 while bus bar 244 can beelectrically coupled with a second (e.g., negative) terminal 248 ofpower source 240.

In some embodiments, IGU 102 includes a plug-in component 250. In someembodiments, plug-in component 250 includes a first electrical input 252(e.g., a pin, socket, or other electrical connector or conductor) thatis electrically coupled with power source terminal 246 via, for example,one or more wires or other electrical connections, components, ordevices. Similarly, plug-in component 250 can include a secondelectrical input 254 that is electrically coupled with power sourceterminal 248 via, for example, one or more wires or other electricalconnections, components, or devices. In some embodiments, firstelectrical input 252 can be electrically coupled with bus bar 242, andfrom there with first conductive layer 230, while second electricalinput 254 can be coupled with bus bar 244, and from there with secondconductive layer 238. The conductive layers 230 and 238 also can beconnected to power source 240 with other conventional means as well asaccording to other means described below with respect to a windowcontroller. For example, as described below with reference to FIG. 9,first electrical input 252 can be connected to a first power line whilesecond electrical input 254 can be connected to a second power line.Additionally, in some embodiments, third electrical input 256 can becoupled to a device, system, or building ground. Furthermore, in someembodiments, fourth and fifth electrical inputs/outputs 258 and 260,respectively, can be used for communication between, for example, awindow controller or microcontroller and a network controller.

In some embodiments, electrical input 252 and electrical input 254receive, carry, or transmit complementary power signals. In someembodiments, electrical input 252 and its complement electrical input254 can be directly connected to the bus bars 242 and 244, respectively,and on the other side, to an external power source that provides avariable DC voltage (e.g., sign and magnitude). The external powersource can be a window controller (see element 114 of FIG. 9) itself, orpower from a building transmitted to a window controller or otherwisecoupled to electrical inputs 252 and 254. In such an embodiment, theelectrical signals transmitted through electrical inputs/outputs 258 and260 can be directly connected to a memory device to allow communicationbetween the window controller and the memory device. Furthermore, insuch an embodiment, the electrical signal input to electrical input 256can be internally connected or coupled (within IGU 102) to eitherelectrical input 252 or 254 or to the bus bars 242 or 244 in such a wayas to enable the electrical potential of one or more of those elementsto be remotely measured (sensed). This can allow the window controllerto compensate for a voltage drop on the connecting wires from the windowcontroller to the electrochromic device 220.

In some embodiments, the window controller can be immediately attached(e.g., external to the IGU 102 but inseparable by the user) orintegrated within the IGU 102. For example, U.S. patent application Ser.No. 13/049,750 (Attorney Docket No. SLDMP008) naming Brown et al. asinventors, titled ONBOARD CONTROLLER FOR MULTISTATE WINDOWS and filed 16Mar. 2011, incorporated by reference herein, describes in detail variousembodiments of an “onboard” controller. In such an embodiment,electrical input 252 can be connected to the positive output of anexternal DC power source. Similarly, electrical input 254 can beconnected to the negative output of the DC power source. As describedbelow, however, electrical inputs 252 and 254 can, alternately, beconnected to the outputs of an external low voltage AC power source(e.g., a typical 24 V AC transformer common to the HVAC industry). Insuch an embodiment, electrical inputs/outputs 258 and 260 can beconnected to the communication bus between the window controller and anetwork controller. In this embodiment, electrical input/output 256 canbe eventually (e.g., at the power source) connected with the earthground (e.g., Protective Earth, or PE in Europe) terminal of the system.

Although the applied voltages may be provided as DC voltages, in someembodiments, the voltages actually supplied by the external power sourceare AC voltage signals. In some other embodiments, the supplied voltagesignals are converted to pulse-width modulated voltage signals. However,the voltages actually “seen” or applied to the bus bars 242 and 244 areeffectively DC voltages. Typically, the voltage oscillations applied atterminals 246 and 248 are in the range of approximately 1 Hz to 1 MHz,and in particular embodiments, approximately 100 kHz. In variousembodiments, the oscillations have asymmetric residence times for thedarkening (e.g., tinting) and lightening (e.g., clearing) portions of aperiod. For example, in some embodiments, transitioning from a firstless transparent state to a second more transparent state requires moretime than the reverse; that is, transitioning from the more transparentsecond state to the less transparent first state. As will be describedbelow, a controller can be designed or configured to apply a drivingvoltage meeting these requirements.

The oscillatory applied voltage control allows the electrochromic device220 to operate in, and transition to and from, one or more stateswithout any necessary modification to the electrochromic device stack220 or to the transitioning time. Rather, the window controller can beconfigured or designed to provide an oscillating drive voltage ofappropriate wave profile, taking into account such factors as frequency,duty cycle, mean voltage, amplitude, among other possible suitable orappropriate factors. Additionally, such a level of control permits thetransitioning to any state over the full range of optical states betweenthe two end states. For example, an appropriately configured controllercan provide a continuous range of transmissivity (% T) which can betuned to any value between end states (e.g., opaque and clear endstates).

To drive the device to an intermediate state using the oscillatorydriving voltage, a controller could simply apply the appropriateintermediate voltage. However, there can be more efficient ways to reachthe intermediate optical state. This is partly because high drivingvoltages can be applied to reach the end states but are traditionallynot applied to reach an intermediate state. One technique for increasingthe rate at which the electrochromic device 220 reaches a desiredintermediate state is to first apply a high voltage pulse suitable forfull transition (to an end state) and then back off to the voltage ofthe oscillating intermediate state (just described). Stated another way,an initial low frequency single pulse (low in comparison to thefrequency employed to maintain the intermediate state) of magnitude andduration chosen for the intended final state can be employed to speedthe transition. After this initial pulse, a higher frequency voltageoscillation can be employed to sustain the intermediate state for aslong as desired.

In some embodiments, each IGU 102 includes a component 250 that is“pluggable” or readily-removable from IGU 102 (e.g., for ease ofmaintenance, manufacture, or replacement). In some particularembodiments, each plug-in component 250 itself includes a windowcontroller. That is, in some such embodiments, each electrochromicdevice 220 is controlled by its own respective local window controllerlocated within plug-in component 250. In some other embodiments, thewindow controller is integrated with another portion of frame 218,between the glass panes in the secondary seal area, or within volume226. In some other embodiments, the window controller can be locatedexternal to IGU 102. In various embodiments, each window controller cancommunicate with the IGUs 102 it controls and drives, as well ascommunicate to other window controllers, the network controller, BMS, orother servers, systems, or devices (e.g., sensors), via one or morewired (e.g., Ethernet) networks or wireless (e.g., WiFi) networks, forexample, via wired (e.g., Ethernet) interface 263 or wireless (WiFi)interface 265. See FIG. 9. Embodiments having Ethernet or Wificapabilities are also well-suited for use in residential homes and othersmaller-scale non-commercial applications. Additionally, thecommunication can be direct or indirect, e.g., via an intermediate nodebetween a master controller such as network controller 112 and the IGU102.

FIG. 9 depicts a window controller 114, which may be deployed as, forexample, component 250. In some embodiments, window controller 114communicates with a network controller over a communication bus 262. Forexample, communication bus 262 can be designed according to theController Area Network (CAN) vehicle bus standard. In such embodiments,first electrical input 252 can be connected to a first power line 264while second electrical input 254 can be connected to a second powerline 266. In some embodiments, as described above, the power signalssent over power lines 264 and 266 are complementary; that is,collectively they represent a differential signal (e.g., a differentialvoltage signal). In some embodiments, line 268 is coupled to a system orbuilding ground (e.g., an Earth Ground). In such embodiments,communication over CAN bus 262 (e.g., between microcontroller 274 andnetwork controller 112) may proceed along first and second communicationlines 270 and 272 transmitted through electrical inputs/outputs 258 and260, respectively, according to the CANopen communication protocol orother suitable open, proprietary, or overlying communication protocol.In some embodiments, the communication signals sent over communicationlines 270 and 272 are complementary; that is, collectively theyrepresent a differential signal (e.g., a differential voltage signal).

In some embodiments, component 250 couples CAN communication bus 262into window controller 114, and in particular embodiments, intomicrocontroller 274. In some such embodiments, microcontroller 274 isalso configured to implement the CANopen communication protocol.Microcontroller 274 is also designed or configured (e.g., programmed) toimplement one or more drive control algorithms in conjunction withpulse-width modulated amplifier or pulse-width modulator (PWM) 276,smart logic 278, and signal conditioner 280. In some embodiments,microcontroller 274 is configured to generate a command signalV_(COMMAND), e.g., in the form of a voltage signal, that is thentransmitted to PWM 276. PWM 276, in turn, generates a pulse-widthmodulated power signal, including first (e.g., positive) componentV_(PW1) and second (e.g., negative) component V_(PW2), based onV_(COMMAND). Power signals V_(PW1) and V_(PW2) are then transmittedover, for example, interface 288, to IGU 102, or more particularly, tobus bars 242 and 244 in order to cause the desired optical transitionsin electrochromic device 220. In some embodiments, PWM 276 is configuredto modify the duty cycle of the pulse-width modulated signals such thatthe durations of the pulses in signals V_(PW1) and V_(PW2) are notequal: for example, PWM 276 pulses V_(PW1) with a first 60% duty cycleand pulses V_(PW2) for a second 40% duty cycle. The duration of thefirst duty cycle and the duration of the second duty cycle collectivelyrepresent the duration, t_(PWM) of each power cycle. In someembodiments, PWM 276 can additionally or alternatively modify themagnitudes of the signal pulses V_(PW1) and V_(PW2).

In some embodiments, microcontroller 274 is configured to generateV_(COMMAND) based on one or more factors or signals such as, forexample, any of the signals received over CAN bus 262 as well as voltageor current feedback signals, V_(FB) and I_(FB) respectively, generatedby PWM 276. In some embodiments, microcontroller 274 determines currentor voltage levels in the electrochromic device 220 based on feedbacksignals I_(FB) or V_(FB), respectively, and adjusts V_(COMMAND)according to one or more rules or algorithms to effect a change in therelative pulse durations (e.g., the relative durations of the first andsecond duty cycles) or amplitudes of power signals V_(PW1) and V_(PW2)to produce voltage profiles as described above. Additionally oralternatively, microcontroller 274 can also adjust V_(COMMAND) inresponse to signals received from smart logic 278 or signal conditioner280. For example, a conditioning signal V_(CON) can be generated bysignal conditioner 280 in response to feedback from one or morenetworked or non-networked devices or sensors, such as, for example, anexterior photosensor or photodetector 282, an interior photosensor orphotodetector 284, a thermal or temperature sensor 286, or a tintcommand signal V_(TC). For example, additional embodiments of signalconditioner 280 and V_(CON) are also described in U.S. patentapplication Ser. No. 13/449,235, filed 17 Apr. 2012, and previouslyincorporated by reference.

In certain embodiments, V_(TC) can be an analog voltage signal between 0V and 10 V that can be used or adjusted by users (such as residents orworkers) to dynamically adjust the tint of an IGU 102 (for example, auser can use a control in a room or zone of building 104 similarly to athermostat to finely adjust or modify a tint of the IGUs 102 in the roomor zone) thereby introducing a dynamic user input into the logic withinmicrocontroller 274 that determines V_(COMMAND). For example, when setin the 0 to 2.5 V range, V_(TC) can be used to cause a transition to a5% T state, while when set in the 2.51 to 5 V range, V_(TC) can be usedto cause a transition to a 20% T state, and similarly for other rangessuch as 5.1 to 7.5 V and 7.51 to 10 V, among other range and voltageexamples. In some embodiments, signal conditioner 280 receives theaforementioned signals or other signals over a communication bus orinterface 290. In some embodiments, PWM 276 also generates V_(COMMAND)based on a signal V_(SMART) received from smart logic 278. In someembodiments, smart logic 278 transmits V_(SMART) over a communicationbus such as, for example, an Inter-Integrated Circuit (I²C) multi-masterserial single-ended computer bus. In some other embodiments, smart logic278 communicates with memory device 292 over a 1-WIRE devicecommunications bus system protocol (by Dallas Semiconductor Corp., ofDallas, Tex.).

In some embodiments, microcontroller 274 includes a processor, chip,card, or board, or a combination of these, which includes logic forperforming one or more control functions. Power and communicationfunctions of microcontroller 274 may be combined in a single chip, forexample, a programmable logic device (PLD) chip or field programmablegate array (FPGA), or similar logic. Such integrated circuits cancombine logic, control and power functions in a single programmablechip. In one embodiment, where one pane 216 has two electrochromicdevices 220 (e.g., on opposite surfaces) or where IGU 102 includes twoor more panes 216 that each include an electrochromic device 220, thelogic can be configured to control each of the two electrochromicdevices 220 independently from the other. However, in one embodiment,the function of each of the two electrochromic devices 220 is controlledin a synergistic fashion, for example, such that each device iscontrolled in order to complement the other. For example, the desiredlevel of light transmission, thermal insulative effect, or otherproperty can be controlled via a combination of states for each of theindividual electrochromic devices 220. For example, one electrochromicdevice may be placed in a tinted state while the other is used forresistive heating, for example, via a transparent electrode of thedevice. In another example, the optical states of the two electrochromicdevices are controlled so that the combined transmissivity is a desiredoutcome.

In general, the logic used to control electrochromic device transitionscan be designed or configured in hardware and/or software. In otherwords, the instructions for controlling the drive circuitry may be hardcoded or provided as software. In may be said that the instructions areprovided by “programming”. Such programming is understood to includelogic of any form including hard coded logic in digital signalprocessors and other devices which have specific algorithms implementedas hardware. Programming is also understood to include software orfirmware instructions that may be executed on a general purposeprocessor. In some embodiments, instructions for controlling applicationof voltage to the bus bars are stored on a memory device associated withthe controller or are provided over a network. Examples of suitablememory devices include semiconductor memory, magnetic memory, opticalmemory, and the like. The computer program code for controlling theapplied voltage can be written in any conventional computer readableprogramming language such as assembly language, C, C++, Pascal, Fortran,and the like. Compiled object code or script is executed by theprocessor to perform the tasks identified in the program.

As described above, in some embodiments, microcontroller 274, or windowcontroller 114 generally, also can have wireless capabilities, such aswireless control and powering capabilities. For example, wirelesscontrol signals, such as radio-frequency (RF) signals or infra-red (IR)signals can be used, as well as wireless communication protocols such asWiFi (mentioned above), Bluetooth, Zigbee, EnOcean, among others, tosend instructions to the microcontroller 274 and for microcontroller 274to send data out to, for example, other window controllers, a networkcontroller 112, or directly to a BMS 110. In various embodiments,wireless communication can be used for at least one of programming oroperating the electrochromic device 220, collecting data or receivinginput from the electrochromic device 220 or the IGU 102 generally,collecting data or receiving input from sensors, as well as using thewindow controller 114 as a relay point for other wirelesscommunications. Data collected from IGU 102 also can include count data,such as a number of times an electrochromic device 220 has beenactivated (cycled), an efficiency of the electrochromic device 220 overtime, among other useful data or performance metrics.

The window controller 114 also can have wireless power capability. Forexample, window controller can have one or more wireless power receiversthat receive transmissions from one or more wireless power transmittersas well as one or more wireless power transmitters that transmit powertransmissions enabling window controller 114 to receive power wirelesslyand to distribute power wirelessly to electrochromic device 220.Wireless power transmission includes, for example, induction, resonanceinduction, RF power transfer, microwave power transfer, and laser powertransfer. For example, U.S. patent application Ser. No. 12/971,576[SLDMP003] naming Rozbicki as inventor, titled WIRELESS POWEREDELECTROCHROMIC WINDOWS and filed 17 Dec. 2010, incorporated by referenceherein, describes in detail various embodiments of wireless powercapabilities.

In order to achieve a desired optical transition, the pulse-widthmodulated power signal is generated such that the positive componentV_(PW1) is supplied to, for example, bus bar 244 during the firstportion of the power cycle, while the negative component V_(PW2) issupplied to, for example, bus bar 242 during the second portion of thepower cycle.

In some cases, depending on the frequency (or inversely the duration) ofthe pulse-width modulated signals, this can result in bus bar 244floating at substantially the fraction of the magnitude of V_(P)w1 thatis given by the ratio of the duration of the first duty cycle to thetotal duration t_(PWM) of the power cycle. Similarly, this can result inbus bar 242 floating at substantially the fraction of the magnitude ofV_(PW2) that is given by the ratio of the duration of the second dutycycle to the total duration t_(PWM) of the power cycle. In this way, insome embodiments, the difference between the magnitudes of thepulse-width modulated signal components V_(PW1) and V_(PW2) is twice theeffective DC voltage across terminals 246 and 248, and consequently,across electrochromic device 220. Said another way, in some embodiments,the difference between the fraction (determined by the relative durationof the first duty cycle) of V_(PW1) applied to bus bar 244 and thefraction (determined by the relative duration of the second duty cycle)of V_(PW2) applied to bus bar 242 is the effective DC voltage V_(EFF)applied to electrochromic device 220. The current IEFF through theload—electromagnetic device 220—is roughly equal to the effectivevoltage VEFF divided by the effective resistance (represented byresistor 316) or impedance of the load.

Those of ordinary skill in the art will also understand that thisdescription is applicable to various types of drive mechanism includingfixed voltage (fixed DC), fixed polarity (time varying DC) or areversing polarity (AC, MF, RF power etc. with a DC bias).

The controller may be configured to monitor voltage and/or current fromthe optically switchable device. In some embodiments, the controller isconfigured to calculate current by measuring voltage across a knownresistor in the driving circuit. Other modes of measuring or calculatingcurrent may be employed. These modes may be digital or analog.

Other Embodiments

Although the foregoing embodiments have been described in some detail tofacilitate understanding, the described embodiments are to be consideredillustrative and not limiting. It will be apparent to one of ordinaryskill in the art that certain changes and modifications can be practicedwithin the scope of the appended claims. For example, while the driveprofiles have been described with reference to electrochromic deviceshaving planar bus bars, they apply to any bus bar orientation in whichbus bars of opposite polarity are separated by distances great enough tocause a significant ohmic voltage drop in a transparent conductor layerfrom one bus bar to another. Further, while the drive profiles have beendescribed with reference to electrochromic devices, they can be appliedto other devices in which bus bars of opposite polarity are disposed atopposite sides of the devices.

1. A method of controlling a first optical transition and a secondoptical transition of an optically switchable device, the methodcomprising: (a) receiving a command to undergo the first opticaltransition from a starting optical state to a first ending opticalstate; (b) applying a first drive parameter to bus bars of the opticallyswitchable device and driving the first optical transition for a firstduration; (c) before the optically switchable device reaches the firstending optical state: (i) receiving a second command to undergo thesecond optical transition to a second ending optical state, and (ii)applying a second drive parameter to the bus bars of the opticallyswitchable device and driving the second optical transition for a secondduration, wherein the second drive parameter is different from the firstdrive parameter, wherein the second drive parameter is determined based,at least in part, on the second ending optical state and an amount ofcharge delivered to the optically switchable device during the firstoptical transition toward the first ending optical state, and whereinthe second optical transition is controlled without considering an opencircuit voltage of the optically switchable device.
 2. The method ofclaim 1, further comprising monitoring an amount of charge delivered tothe optically switchable device during the second optical transition tothe second ending optical state, and ceasing to apply the second driveparameter to bus bars of the optically switchable device based, at leastin part, on the amount of charge delivered to the optically switchabledevice during the second optical transition to the second ending opticalstate.
 3. The method of claim 1, wherein (c)(ii) comprises: after (i),determining the amount of charge delivered to the optically switchabledevice during the first optical transition toward the first endingoptical state, determining a target charge count that is appropriate forcausing the optically switchable device to switch from the startingoptical state to the second ending optical state, monitoring an amountof charge delivered to the optically switchable device during the secondoptical transition to the second ending optical state, and applying thesecond drive parameter to the bus bars of the optically switchabledevice until a net amount of charge delivered to the device during thefirst and second optical transitions reaches the target charge count. 4.The method of claim 1, wherein (c)(ii) comprises: determining orestimating an instantaneous optical state of the optically switchabledevice when the second command was received in (c)(i) based, at least inpart, on the amount of charge delivered to the optically switchabledevice during the first optical transition toward the first endingoptical state, determining a target charge count that is appropriate forcausing the optically switchable device to switch from its instantaneousoptical state to the second ending optical state, monitoring an amountof charge delivered to the optically switchable device during the secondoptical transition to the second ending optical state, and applying thesecond drive parameter to the bus bars of the optically switchabledevice until the charge delivered to the optically switchable deviceduring the second optical transition reaches the target charge count. 5.The method of claim 1, wherein driving the first optical transition in(b) comprises: applying the first drive parameter to the bus bars of theoptically switchable device, determining a target open circuit voltageappropriate for switching the optically switchable device from thestarting optical state to the first ending optical state, anddetermining a target charge count appropriate for switching theoptically switchable device from the starting optical state to the firstending optical state, periodically determining an open circuit voltagebetween the bus bars of the optically switchable device, andperiodically determining the amount of charge delivered to the opticallyswitchable device during the first transition toward the first endingoptical state, and periodically comparing the determined open circuitvoltage to a target open circuit voltage and periodically comparing theamount of charge delivered to the optically switchable device during thefirst transition toward the first ending optical state to a first targetcharge count.
 6. The method of claim 1, further comprising: (d) beforethe optically switchable device reaches the second ending optical state:(i) receiving a third command to undergo a third optical transition to athird ending optical state, and (ii) applying a third drive parameter tothe bus bars of the optically switchable device and driving the thirdoptical transition for a third duration, wherein the third driveparameter is different from the second drive parameter, wherein thethird drive parameter is determined based, at least in part, on thethird ending optical state and an amount of charge delivered to theoptically switchable device during the first optical transition towardthe first ending optical state and during the second optical transitiontoward the second ending optical state, and wherein the third opticaltransition is controlled without considering an open circuit voltage ofthe optically switchable device. 7-13. (canceled)
 14. A method forcontrolling an optical transition in an optically switchable device froma starting optical state to an ending optical state, the methodcomprising: (a) applying a drive voltage to bus bars of the opticallyswitchable device for a duration to cause the optically switchabledevice to transition toward the ending optical state; (b) measuring anopen circuit voltage between the bus bars of the optically switchabledevice; (c) comparing the open circuit voltage to a target open circuitvoltage for the optical transition; (d) comparing the open circuitvoltage to a safe voltage limit for the optically switchable device, andeither (i) increasing the drive voltage in cases where the open circuitvoltage is less than the safe voltage limit for the optically switchabledevice, or (ii) decreasing the drive voltage in cases where the opencircuit voltage is greater than the safe voltage limit for the opticallyswitchable device; (e) repeating at least operations (a)-(c) at leastonce; and (f) determining that the open circuit voltage has reached thetarget open circuit voltage, ceasing application of the drive voltage tothe bus bars of the optically switchable device, and applying a holdvoltage to the bus bars of the optically switchable device to therebymaintain the ending optical state.
 15. The method of claim 14, wherein(b) further comprises measuring an amount of charge delivered to thedevice over the course of the optical transition, wherein (c) furthercomprises comparing the amount of charge delivered to the device overthe course of the optical transition to a target charge count for theoptical transition, and wherein (f) further comprises determining thatthe amount of charge delivered to the optically switchable device hasreached the target charge count before applying the hold voltage to thebus bars of the optically switchable device.
 16. A method oftransitioning a group of optically switchable devices, the methodcomprising: (a) receiving a command to transition the group of opticallyswitchable devices to an ending optical state, wherein the groupcomprises a slowest optically switchable device and a faster opticallyswitchable device, wherein the slowest optically switchable device andthe faster optically switchable device are different sizes and/or havedifferent switching properties; (b) determining a switching time for thegroup of optically switchable devices, the switching time being a timerequired for the slowest optically switchable device to reach the endingoptical state; (c) transitioning the slowest optically switchable deviceto the ending optical state; and (d) during (c), transitioning thefaster optically switchable device to the ending optical state with oneor more pauses during transition, the one or more pauses chosen in timeand duration so as to approximately match an optical state of the fasteroptically switchable device with an optical state of the slowestoptically switchable device during (c).
 17. The method of claim 16,wherein the one or more pauses includes at least two pauses.
 18. Themethod of claim 16, wherein the time and duration of the one or morepauses are determined automatically using an algorithm.
 19. The methodof claim 16, wherein the durations of the one or more pauses aredetermined based on a lookup table.
 20. The method of claim 19, whereinthe lookup table comprises information regarding a size of eachoptically switchable device in the group and/or a switching time foreach optically switchable device in the group.
 21. The method of claim16, wherein a transition on the slowest optically switchable device ismonitored using feedback obtained during the transition on the slowestoptically switchable device.
 22. The method of claim 21, wherein thefeedback obtained during the transition on the slowest opticallyswitchable device comprises one or more parameters selected from thegroup consisting of: an open circuit voltage, a current measured inresponse to an applied voltage, and a charge or charge density deliveredto the slowest optically switchable device.
 23. The method of claim 22,wherein the feedback obtained during the transition on the slowestoptically switchable device comprises the open circuit voltage and thecharge or charge density delivered to the slowest optically switchabledevice.
 24. The method of claim 23, wherein the transition on the fasteroptically switchable device is monitored using feedback obtained duringthe transition on the faster optically switchable device.
 25. The methodof claim 24, wherein the feedback obtained during the transition on thefaster optically switchable device comprises one or more parametersselected from the group consisting of: an open circuit voltage, acurrent measured in response to an applied voltage, and a charge orcharge density delivered to the faster optically switchable device. 26.The method of claim 25, wherein the feedback obtained during thetransition on the faster optically switchable device comprises thecharge or charge density delivered to the faster optically switchabledevice, and does not comprise the open circuit voltage, nor the currentmeasured in response to the applied voltage.
 27. The method of claim 16,wherein the group of optically switchable devices comprises two or morefaster optically switchable devices, and wherein transitioning in (d) isstaggered for the two or more faster optically switchable devices suchthat at least one of the faster optically switchable devices pauseswhile at least one other of the faster optically switchable devicestransitions.
 28. The method of claim 16, further comprising (e) applyinga hold voltage to each device of the group of optically switchabledevices as each device reaches the ending optical state.
 29. The methodof claim 16, further comprising: in response to receiving a command totransition the group of optically switchable devices to a second endingoptical state before the group of optically switchable devices reachesthe ending optical state, transitioning the slowest optically switchabledevice and the faster optically switchable device to the second endingoptical state without any pauses.
 30. The method of claim 16, whereinduring pausing in (d), open circuit conditions are applied to the fasteroptically switchable device.
 31. The method of claim 16, furthercomprising measuring an open circuit voltage on the faster opticallyswitchable device, wherein during pausing in (d), the measured opencircuit voltage is applied to the faster optically switchable device.32. The method of claim 16, wherein during pausing in (d), apre-determined voltage is applied to the faster optically switchabledevice.
 33. The method of claim 16, wherein the group of opticallyswitchable devices comprises optically switchable devices of at leastthree different sizes.
 34. The method of claim 16, wherein the slowestoptically switchable device transitions to the ending optical statewithout pausing.
 35. A method of transitioning a group of opticallyswitchable devices, the method comprising: (a) receiving a command totransition the group of optically switchable devices to an endingoptical state, wherein the group comprises a slowest opticallyswitchable device and a faster optically switchable device, wherein theslowest optically switchable device and the faster optically switchabledevice are different sizes and/or have different switching properties;(b) determining a switching time for the group of optically switchabledevices, the switching time being a time required for the slowestoptically switchable device to reach the ending optical state; (c)transitioning the slowest optically switchable device to the endingoptical state; (d) during (c), transitioning the faster opticallyswitchable device to an intermediate optical state; (e) during (c) andafter (d), maintaining the intermediate optical state on the fasteroptically switchable device for a duration; (f) during (c) and after(e), transitioning the faster optically switchable device to the endingoptical state, wherein the duration in (e) is chosen so as toapproximately match an optical state of the faster optically switchabledevice with an optical state of the slowest optically switchable deviceduring (c).
 36. The method of claim 35, further comprising during (c)and before (f), transitioning the faster optically switchable device toa second intermediate optical state, and then maintaining the secondintermediate optical state for a second duration.
 37. The method ofclaim 35, wherein the duration during (e) is determined automaticallyusing an algorithm.
 38. The method of claim 35, wherein the durationduring (e) is determined automatically based on a lookup table.
 39. Themethod of claim 35, wherein a transition on the slowest opticallyswitchable device is monitored using feedback obtained during thetransition on the slowest optically switchable device.
 40. The method ofclaim 39, wherein the feedback obtained during the transition on theslowest optically switchable device comprises one or more parametersselected from the group consisting of: an open circuit voltage, acurrent measured in response to an applied voltage, and a charge orcharge density delivered to the slowest optically switchable deviceduring the transition on the slowest optically switchable device. 41.The method of claim 40, wherein the feedback obtained during thetransition on the slowest optically switchable device comprises the opencircuit voltage and the charge or charge density delivered to theslowest optically switchable device.
 42. The method of claim 41, whereinduring (f) a transition on the faster optically switchable device to theending optical state is monitored using feedback obtained on the fasteroptically switchable device during (f).
 43. The method of claim 42,wherein the feedback obtained on the faster optically switchable deviceduring (f) comprises one or more parameters selected from the groupconsisting of: an open circuit voltage, a current measured in responseto an applied voltage, and a charge or charge density delivered to thefaster optically switchable device.
 44. The method of claim 43, whereinthe feedback obtained on the faster optically switchable device during(f) comprises the open circuit voltage and the charge or charge densitydelivered to the slowest optically switchable device.
 45. The method ofclaim 35, wherein the group of optically switchable devices comprisestwo or more faster optically switchable devices, and whereintransitioning in (d) and (f) and maintaining in (e) are staggered forthe two or more faster optically switchable devices such that at leastone of the faster optically switchable devices maintains itsintermediate optical state in (e) while at least one other of the fasteroptically switchable devices transitions in (d) and/or (e).
 46. Themethod of claim 35, wherein during maintaining the intermediate opticalstate in (e), open circuit conditions are applied to the fasteroptically switchable device.
 47. The method of claim 35, furthercomprising, measuring an open circuit voltage on the faster opticallyswitchable device, wherein during maintaining the intermediate opticalstate in (e), the measured open circuit voltage is applied to the fasteroptically switchable device.
 48. The method of claim 35, wherein duringmaintaining the intermediate optical state in (e), a pre-determinedvoltage is applied to the faster optically switchable device.
 49. Themethod of claim 35, wherein the group of optically switchable devicescomprises optically switchable devices of at least three differentsizes.
 50. The method of claim 35, wherein the slowest opticallyswitchable device transitions to the ending optical state withoutstopping at any intermediate optical states.
 51. The method of claim 35,further comprising (g) applying a hold voltage to each device of thegroup of optically switchable devices as each device reaches the endingoptical state. 52-87. (canceled)